Cookies: HTTP State Management Mechanism
draft-ietf-httpbis-rfc6265bis-20
| Document | Type | Active Internet-Draft (httpbis WG) | |
|---|---|---|---|
| Authors | Steven Bingler , Mike West , John Wilander | ||
| Last updated | 2025-03-19 (Latest revision 2025-03-17) | ||
| Replaces | draft-ietf-httpbis-cookie-prefixes, draft-thomson-http-omnomnom, draft-ietf-httpbis-cookie-same-site, draft-ietf-httpbis-cookie-alone | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Reviews |
GENART IETF Last Call review
(of
-19)
by Dale Worley
Ready w/issues
ARTART Telechat review
(of
-19)
by Claudio Allocchio
Ready w/issues
DNSDIR Telechat review
(of
-19)
by Petr Špaček
Almost ready
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Associated WG milestone |
|
||
| Document shepherd | Mark Nottingham | ||
| Shepherd write-up | Show Last changed 2025-01-07 | ||
| IESG | IESG state | Approved-announcement to be sent::Revised I-D Needed | |
| Action Holders | |||
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Mike Bishop | ||
| Send notices to | mnot@mnot.net | ||
| IANA | IANA review state | Version Changed - Review Needed |
draft-ietf-httpbis-rfc6265bis-20
HTTP S. Bingler, Ed.
Internet-Draft M. West, Ed.
Obsoletes: 6265 (if approved) Google LLC
Intended status: Standards Track J. Wilander, Ed.
Expires: 18 September 2025 Apple, Inc
17 March 2025
Cookies: HTTP State Management Mechanism
draft-ietf-httpbis-rfc6265bis-20
Abstract
This document defines the HTTP Cookie and Set-Cookie header fields.
These header fields can be used by HTTP servers to store state
(called cookies) at HTTP user agents, letting the servers maintain a
stateful session over the mostly stateless HTTP protocol. Although
cookies have many historical infelicities that degrade their security
and privacy, the Cookie and Set-Cookie header fields are widely used
on the Internet. This document obsoletes RFC 6265.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-httpbis-rfc6265bis/.
Discussion of this document takes place on the HTTP Working Group
mailing list (mailto:ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/. Working Group
information can be found at https://httpwg.org/.
Source for this draft and an issue tracker can be found at
https://github.com/httpwg/http-extensions/labels/6265bis.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Bingler, et al. Expires 18 September 2025 [Page 1]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 18 September 2025.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Conformance Criteria . . . . . . . . . . . . . . . . . . 5
2.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 5
2.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Which Requirements to Implement . . . . . . . . . . . . . 10
3.2.1. Cookie Producing Implementations . . . . . . . . . . 10
3.2.2. Cookie Consuming Implementations . . . . . . . . . . 11
4. Server Requirements . . . . . . . . . . . . . . . . . . . . . 11
4.1. Set-Cookie . . . . . . . . . . . . . . . . . . . . . . . 11
4.1.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . 12
Bingler, et al. Expires 18 September 2025 [Page 2]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
4.1.2. Semantics (Non-Normative) . . . . . . . . . . . . . . 14
4.1.3. Cookie Name Prefixes . . . . . . . . . . . . . . . . 17
4.2. Cookie . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . 18
4.2.2. Semantics . . . . . . . . . . . . . . . . . . . . . . 19
5. User Agent Requirements . . . . . . . . . . . . . . . . . . . 19
5.1. Subcomponent Algorithms . . . . . . . . . . . . . . . . . 20
5.1.1. Dates . . . . . . . . . . . . . . . . . . . . . . . . 20
5.1.2. Canonicalized Host Names . . . . . . . . . . . . . . 22
5.1.3. Domain Matching . . . . . . . . . . . . . . . . . . . 22
5.1.4. Paths and Path-Match . . . . . . . . . . . . . . . . 22
5.2. "Same-site" and "cross-site" Requests . . . . . . . . . . 23
5.2.1. Document-based requests . . . . . . . . . . . . . . . 24
5.2.2. Worker-based requests . . . . . . . . . . . . . . . . 25
5.3. Ignoring Set-Cookie Header Fields . . . . . . . . . . . . 26
5.4. Cookie Name Prefixes . . . . . . . . . . . . . . . . . . 26
5.5. Cookie Lifetime Limits . . . . . . . . . . . . . . . . . 27
5.6. The Set-Cookie Header Field . . . . . . . . . . . . . . . 28
5.6.1. The Expires Attribute . . . . . . . . . . . . . . . . 30
5.6.2. The Max-Age Attribute . . . . . . . . . . . . . . . . 31
5.6.3. The Domain Attribute . . . . . . . . . . . . . . . . 31
5.6.4. The Path Attribute . . . . . . . . . . . . . . . . . 32
5.6.5. The Secure Attribute . . . . . . . . . . . . . . . . 32
5.6.6. The HttpOnly Attribute . . . . . . . . . . . . . . . 32
5.6.7. The SameSite Attribute . . . . . . . . . . . . . . . 32
5.7. Storage Model . . . . . . . . . . . . . . . . . . . . . . 34
5.8. Retrieval Model . . . . . . . . . . . . . . . . . . . . . 40
5.8.1. The Cookie Header Field . . . . . . . . . . . . . . . 40
5.8.2. Non-HTTP APIs . . . . . . . . . . . . . . . . . . . . 41
5.8.3. Retrieval Algorithm . . . . . . . . . . . . . . . . . 41
6. Implementation Considerations . . . . . . . . . . . . . . . . 43
6.1. Limits . . . . . . . . . . . . . . . . . . . . . . . . . 43
6.2. Application Programming Interfaces . . . . . . . . . . . 44
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 44
7.1. Third-Party Cookies . . . . . . . . . . . . . . . . . . . 45
7.2. Cookie Policy . . . . . . . . . . . . . . . . . . . . . . 45
7.3. User Controls . . . . . . . . . . . . . . . . . . . . . . 46
7.4. Expiration Dates . . . . . . . . . . . . . . . . . . . . 46
8. Security Considerations . . . . . . . . . . . . . . . . . . . 47
8.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 47
8.2. Ambient Authority . . . . . . . . . . . . . . . . . . . . 47
8.3. Clear Text . . . . . . . . . . . . . . . . . . . . . . . 48
8.4. Session Identifiers . . . . . . . . . . . . . . . . . . . 49
8.5. Weak Confidentiality . . . . . . . . . . . . . . . . . . 49
8.6. Weak Integrity . . . . . . . . . . . . . . . . . . . . . 50
8.7. Reliance on DNS . . . . . . . . . . . . . . . . . . . . . 51
8.8. SameSite Cookies . . . . . . . . . . . . . . . . . . . . 51
8.8.1. Defense in depth . . . . . . . . . . . . . . . . . . 51
Bingler, et al. Expires 18 September 2025 [Page 3]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
8.8.2. Top-level Navigations . . . . . . . . . . . . . . . . 52
8.8.3. Mashups and Widgets . . . . . . . . . . . . . . . . . 52
8.8.4. Server-controlled . . . . . . . . . . . . . . . . . . 53
8.8.5. Reload navigations . . . . . . . . . . . . . . . . . 53
8.8.6. Top-level requests with "unsafe" methods . . . . . . 54
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 54
9.1. Cookie . . . . . . . . . . . . . . . . . . . . . . . . . 54
9.2. Set-Cookie . . . . . . . . . . . . . . . . . . . . . . . 55
9.3. "Cookie Attributes" Registry . . . . . . . . . . . . . . 55
9.3.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 55
9.3.2. Registration . . . . . . . . . . . . . . . . . . . . 55
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 56
10.1. Normative References . . . . . . . . . . . . . . . . . . 56
10.2. Informative References . . . . . . . . . . . . . . . . . 57
Appendix A. Changes from RFC 6265 . . . . . . . . . . . . . . . 59
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 60
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 60
1. Introduction
This document defines the HTTP Cookie and Set-Cookie header fields.
Using the Set-Cookie header field, an HTTP server can pass name/value
pairs and associated metadata (called cookies) to a user agent. When
the user agent makes subsequent requests to the server, the user
agent uses the metadata and other information to determine whether to
return the name/value pairs in the Cookie header field.
Although simple on their surface, cookies have a number of
complexities. For example, the server indicates a scope for each
cookie when sending it to the user agent. The scope indicates the
maximum amount of time in which the user agent should return the
cookie, the servers to which the user agent should return the cookie,
and the connection types for which the cookie is applicable.
For historical reasons, cookies contain a number of security and
privacy infelicities. For example, a server can indicate that a
given cookie is intended for "secure" connections, but the Secure
attribute does not provide integrity in the presence of an active
network attacker. Similarly, cookies for a given host are shared
across all the ports on that host, even though the usual "same-origin
policy" used by web browsers isolates content retrieved via different
ports.
This specification applies to developers of both cookie-producing
servers and cookie-consuming user agents. Section 3.2 helps to
clarify the intended target audience for each implementation type.
Bingler, et al. Expires 18 September 2025 [Page 4]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
To maximize interoperability with user agents, servers SHOULD limit
themselves to the well-behaved profile defined in Section 4 when
generating cookies.
User agents MUST implement the more liberal processing rules defined
in Section 5, in order to maximize interoperability with existing
servers that do not conform to the well-behaved profile defined in
Section 4.
This document specifies the syntax and semantics of these header
fields as they are actually used on the Internet. In particular,
this document does not create new syntax or semantics beyond those in
use today. The recommendations for cookie generation provided in
Section 4 represent a preferred subset of current server behavior,
and even the more liberal cookie processing algorithm provided in
Section 5 does not recommend all of the syntactic and semantic
variations in use today. Where some existing software differs from
the recommended protocol in significant ways, the document contains a
note explaining the difference.
This document obsoletes [RFC6265].
2. Conventions
2.1. Conformance Criteria
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Requirements phrased in the imperative as part of algorithms (such as
"strip any leading space characters" or "return false and abort these
steps") are to be interpreted with the meaning of the key word
("MUST", "SHOULD", "MAY", etc.) used in introducing the algorithm.
Conformance requirements phrased as algorithms or specific steps can
be implemented in any manner, so long as the end result is
equivalent. In particular, the algorithms defined in this
specification are intended to be easy to understand and are not
intended to be performant.
2.2. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234].
Bingler, et al. Expires 18 September 2025 [Page 5]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
The following core rules are included by reference, as defined in
[RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
(CR LF), CTLs (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), NUL (null octet),
OCTET (any 8-bit sequence of data except NUL), SP (space), HTAB
(horizontal tab), CHAR (any [USASCII] character), VCHAR (any visible
[USASCII] character), and WSP (whitespace).
The OWS (optional whitespace) and BWS (bad whitespace) rules are
defined in Section 5.6.3 of [HTTP].
2.3. Terminology
The terms "user agent", "client", "server", "proxy", and "origin
server" have the same meaning as in the HTTP/1.1 specification
([HTTP], Section 3).
The request-host is the name of the host, as known by the user agent,
to which the user agent is sending an HTTP request or from which it
is receiving an HTTP response (i.e., the name of the host to which it
sent the corresponding HTTP request).
The term request-uri refers to "target URI" as defined in Section 7.1
of [HTTP].
Two sequences of octets are said to case-insensitively match each
other if and only if they are equivalent under the i;ascii-casemap
collation defined in [RFC4790].
The term string means a sequence of non-NUL octets.
The terms "active browsing context", "active document", "ancestor
navigables", "container document", "content navigable", "dedicated
worker", "Document", "inclusive ancestor navigables", "navigable",
"opaque origin", "sandboxed origin browsing context flag", "shared
worker", "the worker's Documents", "top-level traversable", and
"WorkerGlobalScope" are defined in [HTML].
"Service Workers" are defined in the Service Workers specification
[SERVICE-WORKERS].
The term "origin", the mechanism of deriving an origin from a URI,
and the "the same" matching algorithm for origins are defined in
[RFC6454].
"Safe" HTTP methods include GET, HEAD, OPTIONS, and TRACE, as defined
in Section 9.2.1 of [HTTP].
Bingler, et al. Expires 18 September 2025 [Page 6]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
A domain's "public suffix" is the portion of a domain that is
controlled by a public registry, such as "com", "co.uk", and
"pvt.k12.wy.us". A domain's "registrable domain" is the domain's
public suffix plus the label to its left. That is, for
https://www.site.example, the public suffix is example, and the
registrable domain is site.example. Whenever possible, user agents
SHOULD use an up-to-date public suffix list, such as the one
maintained by the Mozilla project at [PSL].
The term "request", as well as a request's "client", "current url",
"method", "target browsing context", and "url list", are defined in
[FETCH].
The term "non-HTTP APIs" refers to non-HTTP mechanisms used to set
and retrieve cookies, such as a web browser API that exposes cookies
to scripts.
The term "top-level navigation" refers to a navigation of a top-level
traversable.
3. Overview
This section outlines a way for an origin server to send state
information to a user agent and for the user agent to return the
state information to the origin server.
To store state, the origin server includes a Set-Cookie header field
in an HTTP response. In subsequent requests, the user agent returns
a Cookie request header field to the origin server. The Cookie
header field contains cookies the user agent received in previous
Set-Cookie header fields. The origin server is free to ignore the
Cookie header field or use its contents for an application-defined
purpose.
Origin servers MAY send a Set-Cookie response header field with any
response. An origin server can include multiple Set-Cookie header
fields in a single response. The presence of a Cookie or a Set-
Cookie header field does not preclude HTTP caches from storing and
reusing a response.
Origin servers and intermediaries MUST NOT combine multiple Set-
Cookie header fields into a single header field. The usual mechanism
for combining HTTP headers fields (i.e., as defined in Section 5.3 of
[HTTP]) might change the semantics of the Set-Cookie header field
because the %x2C (",") character is used by Set-Cookie in a way that
conflicts with such combining.
For example,
Bingler, et al. Expires 18 September 2025 [Page 7]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
Set-Cookie: a=b;path=/c,d=e
is ambiguous. It could be intended as two cookies, a=b and d=e, or a
single cookie with a path of /c,d=e.
User agents MAY ignore Set-Cookie header fields based on response
status codes or the user agent's cookie policy (see Section 5.3).
3.1. Examples
Using the Set-Cookie header field, a server can send the user agent a
short string in an HTTP response that the user agent will return in
future HTTP requests that are within the scope of the cookie. For
example, the server can send the user agent a "session identifier"
named SID with the value 31d4d96e407aad42. The user agent then
returns the session identifier in subsequent requests.
== Server -> User Agent ==
Set-Cookie: SID=31d4d96e407aad42
== User Agent -> Server ==
Cookie: SID=31d4d96e407aad42
The server can alter the default scope of the cookie using the Path
and Domain attributes. For example, the server can instruct the user
agent to return the cookie to every path and every subdomain of
site.example.
== Server -> User Agent ==
Set-Cookie: SID=31d4d96e407aad42; Path=/; Domain=site.example
== User Agent -> Server ==
Cookie: SID=31d4d96e407aad42
As shown in the next example, the server can store multiple cookies
at the user agent. For example, the server can store a session
identifier as well as the user's preferred language by returning two
Set-Cookie header fields. Notice that the server uses the Secure and
HttpOnly attributes to provide additional security protections for
the more sensitive session identifier (see Section 4.1.2).
Bingler, et al. Expires 18 September 2025 [Page 8]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
== Server -> User Agent ==
Set-Cookie: SID=31d4d96e407aad42; Path=/; Secure; HttpOnly
Set-Cookie: lang=en-US; Path=/; Domain=site.example
== User Agent -> Server ==
Cookie: SID=31d4d96e407aad42; lang=en-US
Notice that the Cookie header field above contains two cookies, one
named SID and one named lang.
Cookie names are case-sensitive, meaning that if a server sends the
user agent two Set-Cookie header fields that differ only in their
name's case the user agent will store and return both of those
cookies in subsequent requests.
== Server -> User Agent ==
Set-Cookie: SID=31d4d96e407aad42
Set-Cookie: sid=31d4d96e407aad42
== User Agent -> Server ==
Cookie: SID=31d4d96e407aad42; sid=31d4d96e407aad42
If the server wishes the user agent to persist the cookie over
multiple "sessions" (e.g., user agent restarts), the server can
specify an expiration date in the Expires attribute. Note that the
user agent might delete the cookie before the expiration date if the
user agent's cookie store exceeds its quota or if the user manually
deletes the server's cookie.
== Server -> User Agent ==
Set-Cookie: lang=en-US; Expires=Wed, 09 Jun 2021 10:18:14 GMT
== User Agent -> Server ==
Cookie: SID=31d4d96e407aad42; lang=en-US
Finally, to remove a cookie, the server returns a Set-Cookie header
field with an expiration date in the past. The server will be
successful in removing the cookie only if the Path and the Domain
attribute in the Set-Cookie header field match the values used when
the cookie was created.
Bingler, et al. Expires 18 September 2025 [Page 9]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
== Server -> User Agent ==
Set-Cookie: lang=; Expires=Sun, 06 Nov 1994 08:49:37 GMT
== User Agent -> Server ==
Cookie: SID=31d4d96e407aad42
3.2. Which Requirements to Implement
The upcoming two sections, Section 4 and Section 5, discuss the set
of requirements for two distinct types of implementations. This
section is meant to help guide implementers in determining which set
of requirements best fits their goals. Choosing the wrong set of
requirements could result in a lack of compatibility with other
cookie implementations.
It's important to note that being compatible means different things
depending on the implementer's goals. These differences have built
up over time due to both intentional and unintentional spec changes,
spec interpretations, and historical implementation differences.
This section roughly divides implementers of the cookie spec into two
types, producers and consumers. These are not official terms and are
only used here to help readers develop an intuitive understanding of
the use cases.
3.2.1. Cookie Producing Implementations
An implementer should choose Section 4 whenever cookies are created
and will be sent to a user agent, such as a web browser. These
implementations are frequently referred to as servers by the spec but
that term includes anything which primarily produces cookies. Some
potential examples:
* Server applications hosting a website or API
* Programming languages or software frameworks that support cookies
* Integrated third-party web applications, such as a business
management suite
All these benefit from not only supporting as many user agents as
possible but also supporting other servers. This is useful if a
cookie is produced by a software framework and is later sent back to
a server application which needs to read it. Section 4 advises best
practices that help maximize this sense of compatibility.
Bingler, et al. Expires 18 September 2025 [Page 10]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
See Section 3.2.2.1 for more details on programming languages and
software frameworks.
3.2.2. Cookie Consuming Implementations
An implementer should choose Section 5 whenever cookies are primarily
received from another source. These implementations are referred to
as user agents. Some examples:
* Web browsers
* Tools that support stateful HTTP
* Programming languages or software frameworks that support cookies
Because user agents don't know which servers a user will access, and
whether or not that server is following best practices, users agents
are advised to implement a more lenient set of requirements and to
accept some things that servers are warned against producing.
Section 5 advises best practices that help maximize this sense of
compatibility.
See Section 3.2.2.1 for more details on programming languages and
software frameworks.
3.2.2.1. Programming Languages & Software Frameworks
A programming language or software framework with support for cookies
could reasonably be used to create an application that acts as a
cookie producer, cookie consumer, or both. Because a developer may
want to maximize their compatibility as either a producer or
consumer, these languages or frameworks should strongly consider
supporting both sets of requirements, Section 4 and Section 5, behind
a compatibility mode toggle. This toggle should default to
Section 4's requirements.
Doing so will reduce the chances that a developer's application can
inadvertently create cookies that cannot be read by other servers.
4. Server Requirements
This section describes the syntax and semantics of a well-behaved
profile of the Cookie and Set-Cookie header fields.
4.1. Set-Cookie
The Set-Cookie HTTP response header field is used to send cookies
from the server to the user agent.
Bingler, et al. Expires 18 September 2025 [Page 11]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
4.1.1. Syntax
Informally, the Set-Cookie response header field contains a cookie,
which begins with a name-value-pair, followed by zero or more
attribute-value pairs. Servers conforming to this profile MUST NOT
send Set-Cookie header fields that deviate from the following
grammar:
set-cookie = set-cookie-string
set-cookie-string = BWS cookie-pair *( BWS ";" OWS cookie-av )
cookie-pair = cookie-name BWS "=" BWS cookie-value
cookie-name = token
cookie-value = *cookie-octet / ( DQUOTE *cookie-octet DQUOTE )
cookie-octet = %x21 / %x23-2B / %x2D-3A / %x3C-5B / %x5D-7E
; US-ASCII characters excluding CTLs,
; whitespace, DQUOTE, comma, semicolon,
; and backslash
token = <token, defined in [HTTP], Section 5.6.2>
cookie-av = expires-av / max-age-av / domain-av /
path-av / secure-av / httponly-av /
samesite-av / extension-av
expires-av = "Expires" BWS "=" BWS sane-cookie-date
sane-cookie-date =
<IMF-fixdate, defined in [HTTP], Section 5.6.7>
max-age-av = "Max-Age" BWS "=" BWS non-zero-digit *DIGIT
non-zero-digit = %x31-39
; digits 1 through 9
domain-av = "Domain" BWS "=" BWS domain-value
domain-value = <subdomain>
; see details below
path-av = "Path" BWS "=" BWS path-value
path-value = *av-octet
secure-av = "Secure"
httponly-av = "HttpOnly"
samesite-av = "SameSite" BWS "=" BWS samesite-value
samesite-value = "Strict" / "Lax" / "None"
extension-av = *av-octet
av-octet = %x20-3A / %x3C-7E
; any CHAR except CTLs or ";"
Note that some of the grammatical terms above reference documents
that use different grammatical notations than this document (which
uses ABNF from [RFC5234]).
Per the grammar above, servers MUST NOT produce nameless cookies
(i.e.: an empty cookie-name) as such cookies may be unpredictably
serialized by UAs when sent back to the server.
Bingler, et al. Expires 18 September 2025 [Page 12]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
The semantics of the cookie-value are not defined by this document.
To maximize compatibility with user agents, servers that wish to
store arbitrary data in a cookie-value SHOULD encode that data, for
example, using Base64 [RFC4648].
Per the grammar above, the cookie-value MAY be wrapped in DQUOTE
characters. Note that in this case, the initial and trailing DQUOTE
characters are not stripped. They are part of the cookie-value, and
will be included in Cookie header fields sent to the server.
The domain-value is a subdomain as defined by [RFC1034], Section 3.5,
and as enhanced by [RFC1123], Section 2.1. Thus, domain-value is a
string of [USASCII] characters, such as an "A-label" as defined in
Section 2.3.2.1 of [RFC5890].
The portions of the set-cookie-string produced by the cookie-av term
are known as attributes. To maximize compatibility with user agents,
servers MUST NOT produce two attributes with the same name in the
same set-cookie-string. (See Section 5.7 for how user agents handle
this case.)
NOTE: The name of an attribute-value pair is not case-sensitive. So
while they are presented here in CamelCase, such as "HttpOnly" or
"SameSite", any case is accepted. E.x.: "httponly", "Httponly",
"hTTPoNLY", etc.
Servers MUST NOT include more than one Set-Cookie header field in the
same response with the same cookie-name. (See Section 5.6 for how
user agents handle this case.)
If a server sends multiple responses containing Set-Cookie header
fields concurrently to the user agent (e.g., when communicating with
the user agent over multiple sockets), these responses create a "race
condition" that can lead to unpredictable behavior.
NOTE: Some existing user agents differ in their interpretation of
two-digit years. To avoid compatibility issues, servers SHOULD use
the rfc1123-date format, which requires a four-digit year.
NOTE: Some user agents store and process dates in cookies as 32-bit
UNIX time_t values. Implementation bugs in the libraries supporting
time_t processing on some systems might cause such user agents to
process dates after the year 2038 incorrectly.
Bingler, et al. Expires 18 September 2025 [Page 13]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
4.1.2. Semantics (Non-Normative)
This section describes simplified semantics of the Set-Cookie header
field. These semantics are detailed enough to be useful for
understanding the most common uses of cookies by servers. The full
semantics are described in Section 5.
When the user agent receives a Set-Cookie header field, the user
agent stores the cookie together with its attributes. Subsequently,
when the user agent makes an HTTP request, the user agent includes
the applicable, non-expired cookies in the Cookie header field.
If the user agent receives a new cookie with the same cookie-name,
domain-value, and path-value as a cookie that it has already stored,
the existing cookie is evicted and replaced with the new cookie.
Notice that servers can delete cookies by sending the user agent a
new cookie with an Expires attribute with a value in the past.
Unless the cookie's attributes indicate otherwise, the cookie is
returned only to the origin server (and not, for example, to any
subdomains), and it expires at the end of the current session (as
defined by the user agent). User agents ignore unrecognized cookie
attributes (but not the entire cookie).
4.1.2.1. The Expires Attribute
The Expires attribute indicates the maximum lifetime of the cookie,
represented as the date and time at which the cookie expires. The
user agent may adjust the specified date and is not required to
retain the cookie until that date has passed. In fact, user agents
often evict cookies due to memory pressure or privacy concerns.
4.1.2.2. The Max-Age Attribute
The Max-Age attribute indicates the maximum lifetime of the cookie,
represented as the number of seconds until the cookie expires. The
user agent may adjust the specified duration and is not required to
retain the cookie for that duration. In fact, user agents often
evict cookies due to memory pressure or privacy concerns.
NOTE: Some existing user agents do not support the Max-Age attribute.
User agents that do not support the Max-Age attribute ignore the
attribute.
Bingler, et al. Expires 18 September 2025 [Page 14]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
If a cookie has both the Max-Age and the Expires attribute, the Max-
Age attribute has precedence and controls the expiration date of the
cookie. If a cookie has neither the Max-Age nor the Expires
attribute, the user agent will retain the cookie until "the current
session is over" (as defined by the user agent).
4.1.2.3. The Domain Attribute
The Domain attribute specifies those hosts to which the cookie will
be sent. For example, if the value of the Domain attribute is
"site.example", the user agent will include the cookie in the Cookie
header field when making HTTP requests to site.example,
www.site.example, and www.corp.site.example. (Note that a leading
%x2E ("."), if present, is ignored even though that character is not
permitted.) If the server omits the Domain attribute, the user agent
will return the cookie only to the origin server.
WARNING: Some existing user agents treat an absent Domain attribute
as if the Domain attribute were present and contained the current
host name. For example, if site.example returns a Set-Cookie header
field without a Domain attribute, these user agents will erroneously
send the cookie to www.site.example as well.
The user agent will reject cookies unless the Domain attribute
specifies a scope for the cookie that would include the origin
server. For example, the user agent will accept a cookie with a
Domain attribute of "site.example" or of "foo.site.example" from
foo.site.example, but the user agent will not accept a cookie with a
Domain attribute of "bar.site.example" or of "baz.foo.site.example".
NOTE: For security reasons, many user agents are configured to reject
Domain attributes that correspond to "public suffixes". For example,
some user agents will reject Domain attributes of "com" or "co.uk".
(See Section 5.7 for more information.)
4.1.2.4. The Path Attribute
The scope of each cookie is limited to a set of paths, controlled by
the Path attribute. If the server omits the Path attribute, the user
agent will use the "directory" of the request-uri's path component as
the default value. (See Section 5.1.4 for more details.)
The user agent will include the cookie in an HTTP request only if the
path portion of the request-uri matches (or is a subdirectory of) the
cookie's Path attribute, where the %x2F ("/") character is
interpreted as a directory separator.
Bingler, et al. Expires 18 September 2025 [Page 15]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
Although seemingly useful for isolating cookies between different
paths within a given host, the Path attribute cannot be relied upon
for security (see Section 8).
4.1.2.5. The Secure Attribute
The Secure attribute limits the scope of the cookie to "secure"
channels (where "secure" is defined by the user agent). When a
cookie has the Secure attribute, the user agent will include the
cookie in an HTTP request only if the request is transmitted over a
secure channel (typically HTTP over Transport Layer Security (TLS
[TLS13]) [HTTP]).
4.1.2.6. The HttpOnly Attribute
The HttpOnly attribute limits the scope of the cookie to HTTP
requests. In particular, the attribute instructs the user agent to
omit the cookie when providing access to cookies via non-HTTP APIs.
Note that the HttpOnly attribute is independent of the Secure
attribute: a cookie can have both the HttpOnly and the Secure
attribute.
4.1.2.7. The SameSite Attribute
The "SameSite" attribute limits the scope of the cookie such that it
will only be attached to requests if those requests are same-site, as
defined by the algorithm in Section 5.2. For example, requests for
https://site.example/sekrit-image will attach same-site cookies if
and only if initiated from a context whose "site for cookies" is an
origin with a scheme and registered domain of "https" and
"site.example" respectively.
If the "SameSite" attribute's value is "Strict", the cookie will only
be sent along with "same-site" requests. If the value is "Lax", the
cookie will be sent with same-site requests, and with "cross-site"
top-level navigations, as described in Section 5.6.7.1. If the value
is "None", the cookie will be sent with same-site and cross-site
requests. If the "SameSite" attribute's value is something other
than these three known keywords, the attribute's value will be
subject to a default enforcement mode that is equivalent to "Lax".
If a user agent uses "Lax-allowing-unsafe" enforcement (See
Section 5.6.7.2) then this default enforcement mode will instead be
equivalent to "Lax-allowing-unsafe".
Bingler, et al. Expires 18 September 2025 [Page 16]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
The "SameSite" attribute affects cookie creation as well as delivery.
Cookies which assert "SameSite=Lax" or "SameSite=Strict" cannot be
set in responses to cross-site subresource requests, or cross-site
nested navigations. They can be set along with any top-level
navigation, cross-site or otherwise.
4.1.3. Cookie Name Prefixes
Section 8.5 and Section 8.6 of this document spell out some of the
drawbacks of cookies' historical implementation. In particular, it
is impossible for a server to have confidence that a given cookie was
set with a particular set of attributes. In order to provide such
confidence in a backwards-compatible way, two common sets of
requirements can be inferred from the first few characters of the
cookie's name.
The user agent requirements for the prefixes described below are
detailed in Section 5.4.
To maximize compatibility with user agents servers SHOULD use
prefixes as described below.
4.1.3.1. The "__Secure-" Prefix
If a cookie's name begins with a case-sensitive match for the string
__Secure-, then the cookie will have been set with a Secure
attribute.
For example, the following Set-Cookie header field would be rejected
by a conformant user agent, as it does not have a Secure attribute.
Set-Cookie: __Secure-SID=12345; Domain=site.example
Whereas the following Set-Cookie header field would be accepted if
set from a secure origin (e.g. "https://site.example/"), and rejected
otherwise:
Set-Cookie: __Secure-SID=12345; Domain=site.example; Secure
4.1.3.2. The "__Host-" Prefix
If a cookie's name begins with a case-sensitive match for the string
__Host-, then the cookie will have been set with a Secure attribute,
a Path attribute with a value of /, and no Domain attribute.
This combination yields a cookie that hews as closely as a cookie can
to treating the origin as a security boundary. The lack of a Domain
attribute ensures that the cookie's host-only-flag is true, locking
Bingler, et al. Expires 18 September 2025 [Page 17]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
the cookie to a particular host, rather than allowing it to span
subdomains. Setting the Path to / means that the cookie is effective
for the entire host, and won't be overridden for specific paths. The
Secure attribute ensures that the cookie is unaltered by non-secure
origins, and won't span protocols.
Ports are the only piece of the origin model that __Host- cookies
continue to ignore.
For example, the following cookies would always be rejected:
Set-Cookie: __Host-SID=12345
Set-Cookie: __Host-SID=12345; Secure
Set-Cookie: __Host-SID=12345; Domain=site.example
Set-Cookie: __Host-SID=12345; Domain=site.example; Path=/
Set-Cookie: __Host-SID=12345; Secure; Domain=site.example; Path=/
While the following would be accepted if set from a secure origin
(e.g. "https://site.example/"), and rejected otherwise:
Set-Cookie: __Host-SID=12345; Secure; Path=/
4.2. Cookie
4.2.1. Syntax
The user agent sends stored cookies to the origin server in the
Cookie header field. If the server conforms to the requirements in
Section 4.1 (and the user agent conforms to the requirements in
Section 5), the user agent will send a Cookie header field that
conforms to the following grammar:
cookie = cookie-string
cookie-string = cookie-pair *( ";" SP cookie-pair )
While Section 5.4 of [HTTP] does not define a length limit for header
fields it is likely that the web server's implementation does impose
a limit; many popular implementations have default limits of 8K.
Servers SHOULD avoid setting a large number of large cookies such
that the final cookie-string would exceed their header field limit.
Not doing so could result in requests to the server failing.
Bingler, et al. Expires 18 September 2025 [Page 18]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
Servers MUST be tolerant of multiple cookie headers. For example, an
HTTP/2 [RFC9113] or HTTP/3 [RFC9114] client or intermediary might
split a cookie header to improve compression. Servers are free to
determine what form this tolerance takes. For example, the server
could process each cookie header individually or the server could
concatenate all the cookie headers into one and then process that
final, single, header. The server should be mindful of any header
field limits when deciding which approach to take.
Note: Since intermediaries can modify cookie headers they should also
be mindful of common server header field limits in order to avoid
sending servers headers that they cannot process. For example,
concatenating multiple cookie headers into a single header might
exceed a server's size limit.
4.2.2. Semantics
Each cookie-pair represents a cookie stored by the user agent. The
cookie-pair contains the cookie-name and cookie-value the user agent
received in the Set-Cookie header field.
Notice that the cookie attributes are not returned. In particular,
the server cannot determine from the Cookie field alone when a cookie
will expire, for which hosts the cookie is valid, for which paths the
cookie is valid, or whether the cookie was set with the Secure or
HttpOnly attributes.
The semantics of individual cookies in the Cookie header field are
not defined by this document. Servers are expected to imbue these
cookies with application-specific semantics.
Although cookies are serialized linearly in the Cookie header field,
servers SHOULD NOT rely upon the serialization order. In particular,
if the Cookie header field contains two cookies with the same name
(e.g., that were set with different Path or Domain attributes),
servers SHOULD NOT rely upon the order in which these cookies appear
in the header field.
5. User Agent Requirements
This section specifies the Cookie and Set-Cookie header fields in
sufficient detail that a user agent implementing these requirements
precisely can interoperate with existing servers (even those that do
not conform to the well-behaved profile described in Section 4).
Bingler, et al. Expires 18 September 2025 [Page 19]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
A user agent could enforce more restrictions than those specified
herein (e.g., restrictions specified by its cookie policy, described
in Section 7.2). However, such additional restrictions may reduce
the likelihood that a user agent will be able to interoperate with
existing servers.
5.1. Subcomponent Algorithms
This section defines some algorithms used by user agents to process
specific subcomponents of the Cookie and Set-Cookie header fields.
5.1.1. Dates
The user agent MUST use an algorithm equivalent to the following
algorithm to parse a cookie-date. Note that the various boolean
flags defined as a part of the algorithm (i.e., found-time, found-
day-of-month, found-month, found-year) are initially "not set".
1. Using the grammar below, divide the cookie-date into date-tokens.
cookie-date = *delimiter date-token-list *delimiter
date-token-list = date-token *( 1*delimiter date-token )
date-token = 1*non-delimiter
delimiter = %x09 / %x20-2F / %x3B-40 / %x5B-60 / %x7B-7E
non-delimiter = %x00-08 / %x0A-1F / DIGIT / ":" / ALPHA
/ %x7F-FF
non-digit = %x00-2F / %x3A-FF
day-of-month = 1*2DIGIT [ non-digit *OCTET ]
month = ( "jan" / "feb" / "mar" / "apr" /
"may" / "jun" / "jul" / "aug" /
"sep" / "oct" / "nov" / "dec" ) *OCTET
year = 2*4DIGIT [ non-digit *OCTET ]
time = hms-time [ non-digit *OCTET ]
hms-time = time-field ":" time-field ":" time-field
time-field = 1*2DIGIT
2. Process each date-token sequentially in the order the date-tokens
appear in the cookie-date:
1. If the found-time flag is not set and the token matches the
time production, set the found-time flag and set the hour-
value, minute-value, and second-value to the numbers denoted
by the digits in the date-token, respectively. Skip the
remaining sub-steps and continue to the next date-token.
Bingler, et al. Expires 18 September 2025 [Page 20]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
2. If the found-day-of-month flag is not set and the date-token
matches the day-of-month production, set the found-day-of-
month flag and set the day-of-month-value to the number
denoted by the date-token. Skip the remaining sub-steps and
continue to the next date-token.
3. If the found-month flag is not set and the date-token matches
the month production, set the found-month flag and set the
month-value to the month denoted by the date-token. Skip the
remaining sub-steps and continue to the next date-token.
4. If the found-year flag is not set and the date-token matches
the year production, set the found-year flag and set the
year-value to the number denoted by the date-token. Skip the
remaining sub-steps and continue to the next date-token.
3. If the year-value is greater than or equal to 70 and less than or
equal to 99, increment the year-value by 1900.
4. If the year-value is greater than or equal to 0 and less than or
equal to 69, increment the year-value by 2000.
1. NOTE: Some existing user agents interpret two-digit years
differently.
5. Abort these steps and fail to parse the cookie-date if:
* at least one of the found-day-of-month, found-month, found-
year, or found-time flags is not set,
* the day-of-month-value is less than 1 or greater than 31,
* the year-value is less than 1601,
* the hour-value is greater than 23,
* the minute-value is greater than 59, or
* the second-value is greater than 59.
(Note that leap seconds cannot be represented in this syntax.)
6. Let the parsed-cookie-date be the date whose day-of-month, month,
year, hour, minute, and second (in UTC) are the day-of-month-
value, the month-value, the year-value, the hour-value, the
minute-value, and the second-value, respectively. If no such
date exists, abort these steps and fail to parse the cookie-date.
Bingler, et al. Expires 18 September 2025 [Page 21]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
7. Return the parsed-cookie-date as the result of this algorithm.
5.1.2. Canonicalized Host Names
A canonicalized host name is the string generated by the following
algorithm:
1. Convert the host name to a sequence of individual domain name
labels.
2. Convert each label that is not a Non-Reserved LDH (NR-LDH) label,
to an A-label (see Section 2.3.2.1 of [RFC5890] for the former
and latter).
3. Concatenate the resulting labels, separated by a %x2E (".")
character.
5.1.3. Domain Matching
A string domain-matches a given domain string if at least one of the
following conditions hold:
* The domain string and the string are identical. (Note that both
the domain string and the string will have been canonicalized to
lower case at this point.)
* All of the following conditions hold:
- The domain string is a suffix of the string.
- The last character of the string that is not included in the
domain string is a %x2E (".") character.
- The string is a host name (i.e., not an IP address).
5.1.4. Paths and Path-Match
The user agent MUST use an algorithm equivalent to the following
algorithm to compute the default-path of a cookie:
1. Let uri-path be the path portion of the request-uri if such a
portion exists (and empty otherwise).
2. If the uri-path is empty or if the first character of the uri-
path is not a %x2F ("/") character, output %x2F ("/") and skip
the remaining steps.
Bingler, et al. Expires 18 September 2025 [Page 22]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
3. If the uri-path contains no more than one %x2F ("/") character,
output %x2F ("/") and skip the remaining step.
4. Output the characters of the uri-path from the first character up
to, but not including, the right-most %x2F ("/").
A request-path path-matches a given cookie-path if at least one of
the following conditions holds:
* The cookie-path and the request-path are identical.
Note that this differs from the rules in [RFC3986] for equivalence
of the path component, and hence two equivalent paths can have
different cookies.
* The cookie-path is a prefix of the request-path, and the last
character of the cookie-path is %x2F ("/").
* The cookie-path is a prefix of the request-path, and the first
character of the request-path that is not included in the cookie-
path is a %x2F ("/") character.
5.2. "Same-site" and "cross-site" Requests
Two origins are same-site if they satisfy the "same site" criteria
defined in [SAMESITE]. A request is "same-site" if the following
criteria are true:
1. The request is not the result of a reload navigation triggered
through a user interface element (as defined by the user agent;
e.g., a request triggered by the user clicking a refresh button
on a toolbar).
2. The request's current url's origin is same-site with the
request's client's "site for cookies" (which is an origin), or if
the request has no client or the request's client is null.
Requests which are the result of a reload navigation triggered
through a user interface element are same-site if the reloaded
document was originally navigated to via a same-site request. A
request that is not "same-site" is instead "cross-site".
The request's client's "site for cookies" is calculated depending
upon its client's type, as described in the following subsections:
Bingler, et al. Expires 18 September 2025 [Page 23]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
5.2.1. Document-based requests
The URI displayed in a user agent's address bar is the only security
context directly exposed to users, and therefore the only signal
users can reasonably rely upon to determine whether or not they trust
a particular website. The origin of that URI represents the context
in which a user most likely believes themselves to be interacting.
We'll define this origin, the top-level traversable's active
document's origin, as the "top-level origin".
For a document displayed in a top-level traversable, we can stop
here: the document's "site for cookies" is the top-level origin.
For container documents, we need to audit the origins of each of a
document's ancestor navigables' active documents in order to account
for the "multiple-nested scenarios" described in Section 4 of
[RFC7034]. A document's "site for cookies" is the top-level origin
if and only if the top-level origin is same-site with the document's
origin, and with each of the document's ancestor documents' origins.
Otherwise its "site for cookies" is an origin set to an opaque
origin.
Given a Document (document), the following algorithm returns its
"site for cookies":
1. Let top-document be the active document in document's navigable's
top-level traversable.
2. Let top-origin be the origin of top-document's URI if top-
document's sandboxed origin browsing context flag is set, and
top-document's origin otherwise.
3. Let documents be a list consisting of the active documents of
document's inclusive ancestor navigables.
4. For each item in documents:
1. Let origin be the origin of item's URI if item's sandboxed
origin browsing context flag is set, and item's origin
otherwise.
2. If origin is not same-site with top-origin, return an origin
set to an opaque origin.
5. Return top-origin.
Note: This algorithm only applies when the entire chain of documents
from top-document to document are all active.
Bingler, et al. Expires 18 September 2025 [Page 24]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
5.2.2. Worker-based requests
Worker-driven requests aren't as clear-cut as document-driven
requests, as there isn't a clear link between a top-level traversable
and a worker. This is especially true for Service Workers
[SERVICE-WORKERS], which may execute code in the background, without
any document visible at all.
Note: The descriptions below assume that workers must be same-origin
with the documents that instantiate them. If this invariant changes,
we'll need to take the worker's script's URI into account when
determining their status.
5.2.2.1. Dedicated and Shared Workers
Dedicated workers are simple, as each dedicated worker is bound to
one and only one document. Requests generated from a dedicated
worker (via importScripts, XMLHttpRequest, fetch(), etc) define their
"site for cookies" as that document's "site for cookies".
Shared workers may be bound to multiple documents at once. As it is
quite possible for those documents to have distinct "site for
cookies" values, the worker's "site for cookies" will be an origin
set to an opaque origin in cases where the values are not all same-
site with the worker's origin, and the worker's origin in cases where
the values agree.
Given a WorkerGlobalScope (worker), the following algorithm returns
its "site for cookies":
1. Let site be worker's origin.
2. For each document in worker's Documents:
1. Let document-site be document's "site for cookies" (as
defined in Section 5.2.1).
2. If document-site is not same-site with site, return an origin
set to an opaque origin.
3. Return site.
5.2.2.2. Service Workers
Service Workers are more complicated, as they act as a completely
separate execution context with only tangential relationship to the
Document which registered them.
Bingler, et al. Expires 18 September 2025 [Page 25]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
How user agents handle Service Workers may differ, but user agents
SHOULD match the [SERVICE-WORKERS] specification.
5.3. Ignoring Set-Cookie Header Fields
User agents MAY ignore Set-Cookie header fields contained in
responses with 100-level status codes or based on its cookie policy
(see Section 7.2).
All other Set-Cookie header fields SHOULD be processed according to
Section 5.6. That is, Set-Cookie header fields contained in
responses with non-100-level status codes (including those in
responses with 400- and 500-level status codes) SHOULD be processed
unless ignored according to the user agent's cookie policy.
5.4. Cookie Name Prefixes
User agents' requirements for cookie name prefixes differ slightly
from servers' (Section 4.1.3) in that UAs MUST match the prefix
string case-insensitively.
The normative requirements for the prefixes are detailed in the
storage model algorithm defined in Section 5.7.
This is because some servers will process cookies case-insensitively,
resulting in them unintentionally miscapitalizing and accepting
miscapitalized prefixes.
For example, if a server sends the following Set-Cookie header field
Set-Cookie: __SECURE-SID=12345
to a UA which checks prefixes case-sensitively it will accept this
cookie and the server would incorrectly believe the cookie is subject
the same guarantees as one spelled __Secure-.
Additionally the server is vulnerable to an attacker that
purposefully miscapitalizes a cookie in order to impersonate a
prefixed cookie. For example, a site already has a cookie __Secure-
SID=12345 and by some means an attacker sends the following Set-
Cookie header field for the site to a UA which checks prefixes case-
sensitively.
Set-Cookie: __SeCuRe-SID=evil
The next time a user visits the site the UA will send both cookies:
Cookie: __Secure-SID=12345; __SeCuRe-SID=evil
Bingler, et al. Expires 18 September 2025 [Page 26]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
The server, being case-insensitive, won't be able to tell the
difference between the two cookies allowing the attacker to
compromise the site.
To prevent these issues, UAs MUST match cookie name prefixes case-
insensitive.
Note: Cookies with different names are still considered separate by
UAs. So both __Secure-foo=bar and __secure-foo=baz can exist as
distinct cookies simultaneously and both would have the requirements
of the __Secure- prefix applied.
The following are examples of Set-Cookie header fields that would be
rejected by a conformant user agent.
Set-Cookie: __Secure-SID=12345; Domain=site.example
Set-Cookie: __secure-SID=12345; Domain=site.example
Set-Cookie: __SECURE-SID=12345; Domain=site.example
Set-Cookie: __Host-SID=12345
Set-Cookie: __host-SID=12345; Secure
Set-Cookie: __host-SID=12345; Domain=site.example
Set-Cookie: __HOST-SID=12345; Domain=site.example; Path=/
Set-Cookie: __Host-SID=12345; Secure; Domain=site.example; Path=/
Set-Cookie: __host-SID=12345; Secure; Domain=site.example; Path=/
Set-Cookie: __HOST-SID=12345; Secure; Domain=site.example; Path=/
Whereas the following Set-Cookie header fields would be accepted if
set from a secure origin.
Set-Cookie: __Secure-SID=12345; Domain=site.example; Secure
Set-Cookie: __secure-SID=12345; Domain=site.example; Secure
Set-Cookie: __SECURE-SID=12345; Domain=site.example; Secure
Set-Cookie: __Host-SID=12345; Secure; Path=/
Set-Cookie: __host-SID=12345; Secure; Path=/
Set-Cookie: __HOST-SID=12345; Secure; Path=/
5.5. Cookie Lifetime Limits
When processing cookies with a specified lifetime, either with the
Expires or with the Max-Age attribute, the user agent MUST limit the
maximum age of the cookie. The limit SHOULD NOT be greater than 400
days (34560000 seconds) in the future. The RECOMMENDED limit is 400
days in the future, but the user agent MAY adjust the limit (see
Section 7.2). Expires or Max-Age attributes that specify a lifetime
longer than the limit MUST be reduced to the limit.
Bingler, et al. Expires 18 September 2025 [Page 27]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
5.6. The Set-Cookie Header Field
When a user agent receives a Set-Cookie header field in an HTTP
response, the user agent MAY ignore the Set-Cookie header field in
its entirety (see Section 5.3).
If the user agent does not ignore the Set-Cookie header field in its
entirety, the user agent MUST parse the field-value of the Set-Cookie
header field as a set-cookie-string (defined below).
NOTE: The algorithm below is more permissive than the grammar in
Section 4.1. For example, the algorithm allows cookie-name to be
comprised of cookie-octets instead of being a token as specified in
Section 4.1 and the algorithm accommodates some characters that are
not cookie-octets according to the grammar in Section 4.1. In
addition, the algorithm below also strips leading and trailing
whitespace from the cookie name and value (but maintains internal
whitespace), whereas the grammar in Section 4.1 forbids whitespace in
these positions. User agents use this algorithm so as to
interoperate with servers that do not follow the recommendations in
Section 4.
NOTE: As set-cookie-string may originate from a non-HTTP API, it is
not guaranteed to be free of CTL characters, so this algorithm
handles them explicitly. Horizontal tab (%x09) is excluded from the
CTL characters that lead to set-cookie-string rejection, as it is
considered whitespace, which is handled separately.
NOTE: The set-cookie-string may contain octet sequences that appear
percent-encoded as per Section 2.1 of [RFC3986]. However, a user
agent MUST NOT decode these sequences and instead parse the
individual octets as specified in this algorithm.
A user agent MUST use an algorithm equivalent to the following
algorithm to parse a set-cookie-string:
1. If the set-cookie-string contains a %x00-08 / %x0A-1F / %x7F
character (CTL characters excluding HTAB): Abort these steps and
ignore the set-cookie-string entirely.
2. If the set-cookie-string contains a %x3B (";") character:
1. The name-value-pair string consists of the characters up to,
but not including, the first %x3B (";"), and the unparsed-
attributes consist of the remainder of the set-cookie-string
(including the %x3B (";") in question).
Otherwise:
Bingler, et al. Expires 18 September 2025 [Page 28]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
1. The name-value-pair string consists of all the characters
contained in the set-cookie-string, and the unparsed-
attributes is the empty string.
3. If the name-value-pair string lacks a %x3D ("=") character, then
the name string is empty, and the value string is the value of
name-value-pair.
Otherwise, the (possibly empty) name string consists of the
characters up to, but not including, the first %x3D ("=")
character, and the (possibly empty) value string consists of the
characters after the first %x3D ("=") character.
4. Remove any leading or trailing WSP characters from the name
string and the value string.
5. If the sum of the lengths of the name string and the value string
is more than 4096 octets, abort these steps and ignore the set-
cookie-string entirely.
6. The cookie-name is the name string, and the cookie-value is the
value string.
The user agent MUST use an algorithm equivalent to the following
algorithm to parse the unparsed-attributes:
1. If the unparsed-attributes string is empty, skip the rest of
these steps.
2. Discard the first character of the unparsed-attributes (which
will be a %x3B (";") character).
3. If the remaining unparsed-attributes contains a %x3B (";")
character:
1. Consume the characters of the unparsed-attributes up to, but
not including, the first %x3B (";") character.
Otherwise:
1. Consume the remainder of the unparsed-attributes.
Let the cookie-av string be the characters consumed in this step.
4. If the cookie-av string contains a %x3D ("=") character:
Bingler, et al. Expires 18 September 2025 [Page 29]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
1. The (possibly empty) attribute-name string consists of the
characters up to, but not including, the first %x3D ("=")
character, and the (possibly empty) attribute-value string
consists of the characters after the first %x3D ("=")
character.
Otherwise:
1. The attribute-name string consists of the entire cookie-av
string, and the attribute-value string is empty.
5. Remove any leading or trailing WSP characters from the attribute-
name string and the attribute-value string.
6. If the attribute-value is longer than 1024 octets, ignore the
cookie-av string and return to Step 1 of this algorithm.
7. Process the attribute-name and attribute-value according to the
requirements in the following subsections. (Notice that
attributes with unrecognized attribute-names are ignored.)
8. Return to Step 1 of this algorithm.
When the user agent finishes parsing the set-cookie-string, the user
agent is said to "receive a cookie" from the request-uri with name
cookie-name, value cookie-value, and attributes cookie-attribute-
list. (See Section 5.7 for additional requirements triggered by
receiving a cookie.)
5.6.1. The Expires Attribute
If the attribute-name case-insensitively matches the string
"Expires", the user agent MUST process the cookie-av as follows.
1. Let the expiry-time be the result of parsing the attribute-value
as cookie-date (see Section 5.1.1).
2. If the attribute-value failed to parse as a cookie date, ignore
the cookie-av.
3. Let cookie-age-limit be the maximum age of the cookie (which
SHOULD be 400 days in the future or sooner, see Section 5.5).
4. If the expiry-time is more than cookie-age-limit, the user agent
MUST set the expiry time to cookie-age-limit in seconds.
Bingler, et al. Expires 18 September 2025 [Page 30]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
5. If the expiry-time is earlier than the earliest date the user
agent can represent, the user agent MAY replace the expiry-time
with the earliest representable date.
6. Append an attribute to the cookie-attribute-list with an
attribute-name of Expires and an attribute-value of expiry-time.
5.6.2. The Max-Age Attribute
If the attribute-name case-insensitively matches the string "Max-
Age", the user agent MUST process the cookie-av as follows.
1. If the attribute-value is empty, ignore the cookie-av.
2. If the first character of the attribute-value is neither a DIGIT,
nor a "-" character followed by a DIGIT, ignore the cookie-av.
3. If the remainder of attribute-value contains a non-DIGIT
character, ignore the cookie-av.
4. Let delta-seconds be the attribute-value converted to a base 10
integer.
5. Let cookie-age-limit be the maximum age of the cookie (which
SHOULD be 400 days or less, see Section 5.5).
6. Set delta-seconds to the smaller of its present value and cookie-
age-limit.
7. If delta-seconds is less than or equal to zero (0), let expiry-
time be the earliest representable date and time. Otherwise, let
the expiry-time be the current date and time plus delta-seconds
seconds.
8. Append an attribute to the cookie-attribute-list with an
attribute-name of Max-Age and an attribute-value of expiry-time.
5.6.3. The Domain Attribute
If the attribute-name case-insensitively matches the string "Domain",
the user agent MUST process the cookie-av as follows.
1. Let cookie-domain be the attribute-value.
2. If cookie-domain starts with %x2E ("."), let cookie-domain be
cookie-domain without its leading %x2E (".").
3. Convert the cookie-domain to lower case.
Bingler, et al. Expires 18 September 2025 [Page 31]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
4. Append an attribute to the cookie-attribute-list with an
attribute-name of Domain and an attribute-value of cookie-domain.
5.6.4. The Path Attribute
If the attribute-name case-insensitively matches the string "Path",
the user agent MUST process the cookie-av as follows.
1. If the attribute-value is empty or if the first character of the
attribute-value is not %x2F ("/"):
1. Let cookie-path be the default-path.
Otherwise:
1. Let cookie-path be the attribute-value.
2. Append an attribute to the cookie-attribute-list with an
attribute-name of Path and an attribute-value of cookie-path.
5.6.5. The Secure Attribute
If the attribute-name case-insensitively matches the string "Secure",
the user agent MUST append an attribute to the cookie-attribute-list
with an attribute-name of Secure and an empty attribute-value.
5.6.6. The HttpOnly Attribute
If the attribute-name case-insensitively matches the string
"HttpOnly", the user agent MUST append an attribute to the cookie-
attribute-list with an attribute-name of HttpOnly and an empty
attribute-value.
5.6.7. The SameSite Attribute
If the attribute-name case-insensitively matches the string
"SameSite", the user agent MUST process the cookie-av as follows:
1. Let enforcement be "Default".
2. If cookie-av's attribute-value is a case-insensitive match for
"None", set enforcement to "None".
3. If cookie-av's attribute-value is a case-insensitive match for
"Strict", set enforcement to "Strict".
4. If cookie-av's attribute-value is a case-insensitive match for
"Lax", set enforcement to "Lax".
Bingler, et al. Expires 18 September 2025 [Page 32]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
5. Append an attribute to the cookie-attribute-list with an
attribute-name of "SameSite" and an attribute-value of
enforcement.
5.6.7.1. "Strict" and "Lax" enforcement
Same-site cookies in "Strict" enforcement mode will not be sent along
with top-level navigations which are triggered from a cross-site
document context. As discussed in Section 8.8.2, this might or might
not be compatible with existing session management systems. In the
interests of providing a drop-in mechanism that mitigates the risk of
CSRF attacks, developers may set the SameSite attribute in a "Lax"
enforcement mode that carves out an exception which sends same-site
cookies along with cross-site requests if and only if they are top-
level navigations which use a "safe" (in the [HTTP] sense) HTTP
method. (Note that a request's method may be changed from POST to
GET for some redirects (see Sections 15.4.2 and 15.4.3 of [HTTP]); in
these cases, a request's "safe"ness is determined based on the method
of the current redirect hop.)
Lax enforcement provides reasonable defense in depth against CSRF
attacks that rely on unsafe HTTP methods (like POST), but does not
offer a robust defense against CSRF as a general category of attack:
1. Attackers can still pop up new windows or trigger top-level
navigations in order to create a "same-site" request (as
described in Section 5.2.1), which is only a speedbump along the
road to exploitation.
2. Features like <link rel='prerender'> [prerendering] can be
exploited to create "same-site" requests without the risk of user
detection.
Developers can more completely mitigate CSRF through a session
management mechanism such as that described in Section 8.8.2.
5.6.7.2. "Lax-Allowing-Unsafe" enforcement
As discussed in Section 8.8.6, compatibility concerns may necessitate
the use of a "Lax-allowing-unsafe" enforcement mode that allows
cookies to be sent with a cross-site HTTP request if and only if it
is a top-level request, regardless of request method. That is, the
"Lax-allowing-unsafe" enforcement mode waives the requirement for the
HTTP request's method to be "safe" in the SameSite enforcement step
of the retrieval algorithm in Section 5.8.3. (All cookies,
regardless of SameSite enforcement mode, may be set for top-level
navigations, regardless of HTTP request method, as specified in
Section 5.7.)
Bingler, et al. Expires 18 September 2025 [Page 33]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
"Lax-allowing-unsafe" is not a distinct value of the SameSite
attribute. Rather, user agents MAY apply "Lax-allowing-unsafe"
enforcement only to cookies that did not explicitly specify a
SameSite attribute (i.e., those whose same-site-flag was set to
"Default" by default). To limit the scope of this compatibility
mode, user agents which apply "Lax-allowing-unsafe" enforcement
SHOULD restrict the enforcement to cookies which were created
recently. Deployment experience has shown a cookie age of 2 minutes
or less to be a reasonable limit.
If the user agent uses "Lax-allowing-unsafe" enforcement, it MUST
apply the following modification to the retrieval algorithm defined
in Section 5.8.3:
Replace the condition in the penultimate bullet point of step 1 of
the retrieval algorithm reading
* The HTTP request associated with the retrieval uses a "safe"
method.
with
* At least one of the following is true:
1. The HTTP request associated with the retrieval uses a "safe"
method.
2. The cookie's same-site-flag is "Default" and the amount of
time elapsed since the cookie's creation-time is at most a
duration of the user agent's choosing.
5.7. Storage Model
The user agent stores the following fields about each cookie: name,
value, expiry-time, domain, path, creation-time, last-access-time,
persistent-flag, host-only-flag, secure-only-flag, http-only-flag,
and same-site-flag.
When the user agent "receives a cookie" from a request-uri with name
cookie-name, value cookie-value, and attributes cookie-attribute-
list, the user agent MUST process the cookie as follows:
1. A user agent MAY ignore a received cookie in its entirety. See
Section 5.3.
2. If cookie-name is empty and cookie-value is empty, abort these
steps and ignore the cookie entirely.
Bingler, et al. Expires 18 September 2025 [Page 34]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
3. If the cookie-name or the cookie-value contains a %x00-08 /
%x0A-1F / %x7F character (CTL characters excluding HTAB), abort
these steps and ignore the cookie entirely.
4. If the sum of the lengths of cookie-name and cookie-value is
more than 4096 octets, abort these steps and ignore the cookie
entirely.
5. Create a new cookie with name cookie-name, value cookie-value.
Set the creation-time and the last-access-time to the current
date and time.
6. If the cookie-attribute-list contains an attribute with an
attribute-name of "Max-Age":
1. Set the cookie's persistent-flag to true.
2. Set the cookie's expiry-time to attribute-value of the last
attribute in the cookie-attribute-list with an attribute-
name of "Max-Age".
Otherwise, if the cookie-attribute-list contains an attribute
with an attribute-name of "Expires" (and does not contain an
attribute with an attribute-name of "Max-Age"):
1. Set the cookie's persistent-flag to true.
2. Set the cookie's expiry-time to attribute-value of the last
attribute in the cookie-attribute-list with an attribute-
name of "Expires".
Otherwise:
1. Set the cookie's persistent-flag to false.
2. Set the cookie's expiry-time to the latest representable
date.
7. If the cookie-attribute-list contains an attribute with an
attribute-name of "Domain":
1. Let the domain-attribute be the attribute-value of the last
attribute in the cookie-attribute-list with both an
attribute-name of "Domain" and an attribute-value whose
length is no more than 1024 octets. (Note that a leading
%x2E ("."), if present, is ignored even though that
character is not permitted.)
Bingler, et al. Expires 18 September 2025 [Page 35]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
Otherwise:
1. Let the domain-attribute be the empty string.
8. If the domain-attribute contains a character that is not in the
range of [USASCII] characters, abort these steps and ignore the
cookie entirely.
9. If the user agent is configured to reject "public suffixes" and
the domain-attribute is a public suffix:
1. If the domain-attribute is identical to the canonicalized
request-host:
1. Let the domain-attribute be the empty string.
Otherwise:
1. Abort these steps and ignore the cookie entirely.
NOTE: This step prevents attacker.example from disrupting the
integrity of site.example by setting a cookie with a Domain
attribute of "example".
10. If the domain-attribute is non-empty:
1. If the canonicalized request-host does not domain-match the
domain-attribute:
1. Abort these steps and ignore the cookie entirely.
Otherwise:
1. Set the cookie's host-only-flag to false.
2. Set the cookie's domain to the domain-attribute.
Otherwise:
1. Set the cookie's host-only-flag to true.
2. Set the cookie's domain to the canonicalized request-host.
Bingler, et al. Expires 18 September 2025 [Page 36]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
11. If the cookie-attribute-list contains an attribute with an
attribute-name of "Path", set the cookie's path to attribute-
value of the last attribute in the cookie-attribute-list with
both an attribute-name of "Path" and an attribute-value whose
length is no more than 1024 octets. Otherwise, set the cookie's
path to the default-path of the request-uri.
12. If the cookie-attribute-list contains an attribute with an
attribute-name of "Secure", set the cookie's secure-only-flag to
true. Otherwise, set the cookie's secure-only-flag to false.
13. If the request-uri does not denote a "secure" connection (as
defined by the user agent), and the cookie's secure-only-flag is
true, then abort these steps and ignore the cookie entirely.
14. If the cookie-attribute-list contains an attribute with an
attribute-name of "HttpOnly", set the cookie's http-only-flag to
true. Otherwise, set the cookie's http-only-flag to false.
15. If the cookie was received from a "non-HTTP" API and the
cookie's http-only-flag is true, abort these steps and ignore
the cookie entirely.
16. If the cookie's secure-only-flag is false, and the request-uri
does not denote a "secure" connection, then abort these steps
and ignore the cookie entirely if the cookie store contains one
or more cookies that meet all of the following criteria:
1. Their name matches the name of the newly-created cookie.
2. Their secure-only-flag is true.
3. Their domain domain-matches the domain of the newly-created
cookie, or vice-versa.
4. The path of the newly-created cookie path-matches the path
of the existing cookie.
Note: The path comparison is not symmetric, ensuring only that a
newly-created, non-secure cookie does not overlay an existing
secure cookie, providing some mitigation against cookie-fixing
attacks. That is, given an existing secure cookie named 'a'
with a path of '/login', a non-secure cookie named 'a' could be
set for a path of '/' or '/foo', but not for a path of '/login'
or '/login/en'.
Bingler, et al. Expires 18 September 2025 [Page 37]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
17. If the cookie-attribute-list contains an attribute with an
attribute-name of "SameSite", and an attribute-value of
"Strict", "Lax", or "None", set the cookie's same-site-flag to
the attribute-value of the last attribute in the cookie-
attribute-list with an attribute-name of "SameSite". Otherwise,
set the cookie's same-site-flag to "Default".
18. If the cookie's same-site-flag is not "None":
1. If the cookie was received from a "non-HTTP" API, and the
API was called from a navigable's active document whose
"site for cookies" is not same-site with the top-level
origin, then abort these steps and ignore the newly created
cookie entirely.
2. If the cookie was received from a "same-site" request (as
defined in Section 5.2), skip the remaining substeps and
continue processing the cookie.
3. If the cookie was received from a request which is
navigating a top-level traversable [HTML] (e.g. if the
request's "reserved client" is either null or an environment
whose "target browsing context"'s navigable is a top-level
traversable), skip the remaining substeps and continue
processing the cookie.
Note: Top-level navigations can create a cookie with any
SameSite value, even if the new cookie wouldn't have been
sent along with the request had it already existed prior to
the navigation.
4. Abort these steps and ignore the newly created cookie
entirely.
19. If the cookie's "same-site-flag" is "None", abort these steps
and ignore the cookie entirely unless the cookie's secure-only-
flag is true.
20. If the cookie-name begins with a case-insensitive match for the
string "__Secure-", abort these steps and ignore the cookie
entirely unless the cookie's secure-only-flag is true.
21. If the cookie-name begins with a case-insensitive match for the
string "__Host-", abort these steps and ignore the cookie
entirely unless the cookie meets all the following criteria:
1. The cookie's secure-only-flag is true.
Bingler, et al. Expires 18 September 2025 [Page 38]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
2. The cookie's host-only-flag is true.
3. The cookie-attribute-list contains an attribute with an
attribute-name of "Path", and the cookie's path is /.
22. If the cookie-name is empty and either of the following
conditions are true, abort these steps and ignore the cookie
entirely:
* the cookie-value begins with a case-insensitive match for the
string "__Secure-"
* the cookie-value begins with a case-insensitive match for the
string "__Host-"
23. If the cookie store contains a cookie with the same name,
domain, host-only-flag, and path as the newly-created cookie:
1. Let old-cookie be the existing cookie with the same name,
domain, host-only-flag, and path as the newly-created
cookie. (Notice that this algorithm maintains the invariant
that there is at most one such cookie.)
2. If the newly-created cookie was received from a "non-HTTP"
API and the old-cookie's http-only-flag is true, abort these
steps and ignore the newly created cookie entirely.
3. Update the creation-time of the newly-created cookie to
match the creation-time of the old-cookie.
4. Remove the old-cookie from the cookie store.
24. Insert the newly-created cookie into the cookie store.
A cookie is "expired" if the cookie has an expiry date in the past.
The user agent MUST evict all expired cookies from the cookie store
if, at any time, an expired cookie exists in the cookie store.
At any time, the user agent MAY "remove excess cookies" from the
cookie store if the number of cookies sharing a domain field exceeds
some implementation-defined upper bound (such as 50 cookies).
At any time, the user agent MAY "remove excess cookies" from the
cookie store if the cookie store exceeds some predetermined upper
bound (such as 3000 cookies).
Bingler, et al. Expires 18 September 2025 [Page 39]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
When the user agent removes excess cookies from the cookie store, the
user agent MUST evict cookies in the following priority order:
1. Expired cookies.
2. Cookies whose secure-only-flag is false, and which share a domain
field with more than a predetermined number of other cookies.
3. Cookies that share a domain field with more than a predetermined
number of other cookies.
4. All cookies.
If two cookies have the same removal priority, the user agent MUST
evict the cookie with the earliest last-access-time first.
When "the current session is over" (as defined by the user agent),
the user agent MUST remove from the cookie store all cookies with the
persistent-flag set to false.
5.8. Retrieval Model
This section defines how cookies are retrieved from a cookie store in
the form of a cookie-string. A "retrieval" is any event which
requires generating a cookie-string. For example, a retrieval may
occur in order to build a Cookie header field for an HTTP request, or
may be required in order to return a cookie-string from a call to a
"non-HTTP" API that provides access to cookies. A retrieval has an
associated URI, same-site status, and type, which are defined below
depending on the type of retrieval.
5.8.1. The Cookie Header Field
The user agent includes stored cookies in the Cookie HTTP request
header field.
A user agent MAY omit the Cookie header field in its entirety. For
example, the user agent might wish to block sending cookies during
"third-party" requests from setting cookies (see Section 7.1).
If the user agent does attach a Cookie header field to an HTTP
request, the user agent MUST generate a single cookie-string and the
user agent MUST compute the cookie-string following the algorithm
defined in Section 5.8.3, where the retrieval's URI is the request-
uri, the retrieval's same-site status is computed for the HTTP
request as defined in Section 5.2, and the retrieval's type is
"HTTP".
Bingler, et al. Expires 18 September 2025 [Page 40]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
Note: Previous versions of this specification required that only one
Cookie header field be sent in requests. This is no longer a
requirement. While this specification requires that a single cookie-
string be produced, some user agents may split that string across
multiple cookie header fields. For examples, see Section 8.2.3 of
[RFC9113] and Section 4.2.1 of [RFC9114].
5.8.2. Non-HTTP APIs
The user agent MAY implement "non-HTTP" APIs that can be used to
access stored cookies.
A user agent MAY return an empty cookie-string in certain contexts,
such as when a retrieval occurs within a third-party context (see
Section 7.1).
If a user agent does return cookies for a given call to a "non-HTTP"
API with an associated Document, then the user agent MUST compute the
cookie-string following the algorithm defined in Section 5.8.3, where
the retrieval's URI is defined by the caller (see
[DOM-DOCUMENT-COOKIE]), the retrieval's same-site status is "same-
site" if the Document's "site for cookies" is same-site with the top-
level origin as defined in Section 5.2.1 (otherwise it is "cross-
site"), and the retrieval's type is "non-HTTP".
5.8.3. Retrieval Algorithm
Given a cookie store and a retrieval, the following algorithm returns
a cookie-string from a given cookie store.
1. Let cookie-list be the set of cookies from the cookie store that
meets all of the following requirements:
* Either:
- The cookie's host-only-flag is true and the canonicalized
host of the retrieval's URI is identical to the cookie's
domain.
Or:
- The cookie's host-only-flag is false and the canonicalized
host of the retrieval's URI domain-matches the cookie's
domain.
NOTE: (For user agents configured to reject "public suffixes")
It's possible that the public suffix list was changed since a
cookie was created. If this change results in a cookie's
Bingler, et al. Expires 18 September 2025 [Page 41]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
domain becoming a public suffix then that cookie is considered
invalid as it would have been rejected during creation (See
Section 5.7 step 9). User agents should be careful to avoid
retrieving these invalid cookies even if they domain-match the
host of the retrieval's URI.
* The retrieval's URI's path path-matches the cookie's path.
* If the cookie's secure-only-flag is true, then the retrieval's
URI must denote a "secure" connection (as defined by the user
agent).
NOTE: The notion of a "secure" connection is not defined by
this document. Typically, user agents consider a connection
secure if the connection makes use of transport-layer
security, such as SSL or TLS [TLS13], or if the host is
trusted. For example, most user agents consider "https" to be
a scheme that denotes a secure protocol and "localhost" to be
trusted host.
* If the cookie's http-only-flag is true, then exclude the
cookie if the retrieval's type is "non-HTTP".
* If the cookie's same-site-flag is not "None" and the
retrieval's same-site status is "cross-site", then exclude the
cookie unless all of the following conditions are met:
- The retrieval's type is "HTTP".
- The same-site-flag is "Lax" or "Default".
- The HTTP request associated with the retrieval uses a
"safe" method.
- The target browsing context of the HTTP request associated
with the retrieval is the active browsing context or a top-
level traversable.
2. The user agent SHOULD sort the cookie-list in the following
order:
* Cookies with longer paths are listed before cookies with
shorter paths.
* Among cookies that have equal-length path fields, cookies with
earlier creation-times are listed before cookies with later
creation-times.
Bingler, et al. Expires 18 September 2025 [Page 42]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
NOTE: Not all user agents sort the cookie-list in this order, but
this order reflects common practice when this document was
written, and, historically, there have been servers that
(erroneously) depended on this order.
3. Update the last-access-time of each cookie in the cookie-list to
the current date and time.
4. Serialize the cookie-list into a cookie-string by processing each
cookie in the cookie-list in order:
1. If the cookies' name is not empty, output the cookie's name
followed by the %x3D ("=") character.
2. If the cookies' value is not empty, output the cookie's
value.
3. If there is an unprocessed cookie in the cookie-list, output
the characters %x3B and %x20 ("; ").
6. Implementation Considerations
6.1. Limits
Practical user agent implementations have limits on the number and
size of cookies that they can store. General-use user agents SHOULD
provide each of the following minimum capabilities:
* At least 50 cookies per domain.
* At least 3000 cookies total.
User agents MAY limit the maximum number of cookies they store, and
may evict any cookie at any time (whether at the request of the user
or due to implementation limitations).
Note that a limit on the maximum number of cookies also limits the
total size of the stored cookies, due to the length limits which MUST
be enforced in Section 5.6.
Servers SHOULD use as few and as small cookies as possible to avoid
reaching these implementation limits, minimize network bandwidth due
to the Cookie header field being included in every request, and to
avoid reaching server header field limits (See Section 4.2.1).
Servers SHOULD gracefully degrade if the user agent fails to return
one or more cookies in the Cookie header field because the user agent
might evict any cookie at any time.
Bingler, et al. Expires 18 September 2025 [Page 43]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
6.2. Application Programming Interfaces
One reason the Cookie and Set-Cookie header fields use such esoteric
syntax is that many platforms (both in servers and user agents)
provide a string-based application programming interface (API) to
cookies, requiring application-layer programmers to generate and
parse the syntax used by the Cookie and Set-Cookie header fields,
which many programmers have done incorrectly, resulting in
interoperability problems.
Instead of providing string-based APIs to cookies, platforms would be
well-served by providing more semantic APIs. It is beyond the scope
of this document to recommend specific API designs, but there are
clear benefits to accepting an abstract "Date" object instead of a
serialized date string.
7. Privacy Considerations
Cookies' primary privacy risk is their ability to correlate user
activity. This can happen on a single site, but is most problematic
when activity is tracked across different, seemingly unconnected Web
sites to build a user profile.
Over time, this capability (warned against explicitly in [RFC2109]
and all of its successors) has become widely used for varied reasons
including:
* authenticating users across sites,
* assembling information on users,
* protecting against fraud and other forms of undesirable traffic,
* targeting advertisements at specific users or at users with
specified attributes,
* measuring how often ads are shown to users, and
* recognizing when an ad resulted in a change in user behavior.
While not every use of cookies is necessarily problematic for
privacy, their potential for abuse has become a widespread concern in
the Internet community and broader society. In response to these
concerns, user agents have actively constrained cookie functionality
in various ways (as allowed and encouraged by previous
specifications), while avoiding disruption to features they judge
desirable for the health of the Web.
Bingler, et al. Expires 18 September 2025 [Page 44]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
It is too early to declare consensus on which specific mechanism(s)
should be used to mitigate cookies' privacy impact; user agents'
ongoing changes to how they are handled are best characterised as
experiments that can provide input into that eventual consensus.
Instead, this document describes limited, general mitigations against
the privacy risks associated with cookies that enjoy wide deployment
at the time of writing. It is expected that implementations will
continue to experiment and impose stricter, more well-defined
limitations on cookies over time. Future versions of this document
might codify those mechanisms based upon deployment experience. If
functions that currently rely on cookies can be supported by
separate, targeted mechanisms, they might be documented in separate
specifications and stricter limitations on cookies might become
feasible.
Note that cookies are not the only mechanism that can be used to
track users across sites, so while these mitigations are necessary to
improve Web privacy, they are not sufficient on their own.
7.1. Third-Party Cookies
A "third-party" or cross-site cookie is one that is associated with
embedded content (such as scripts, images, stylesheets, frames) that
is obtained from a different server than the one that hosts the
primary resource (usually, the Web page that the user is viewing).
Third-party cookies are often used to correlate users' activity on
different sites.
Because of their inherent privacy issues, most user agents now limit
third-party cookies in a variety of ways. Some completely block
third-party cookies by refusing to process third-party Set-Cookie
header fields and refusing to send third-party Cookie header fields.
Some partition cookies based upon the first-party context, so that
different cookies are sent depending on the site being browsed. Some
block cookies based upon user agent cookie policy and/or user
controls.
While this document does not endorse or require a specific approach,
it is RECOMMENDED that user agents adopt a policy for third-party
cookies that is as restrictive as compatibility constraints permit.
Consequently, resources cannot rely upon third-party cookies being
treated consistently by user agents for the foreseeable future.
7.2. Cookie Policy
User agents MAY enforce a cookie policy consisting of restrictions on
how cookies may be used or ignored (see Section 5.3).
Bingler, et al. Expires 18 September 2025 [Page 45]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
A cookie policy may govern which domains or parties, as in first and
third parties (see Section 7.1), for which the user agent will allow
cookie access. The policy can also define limits on cookie size,
cookie expiry (see Section 5.5), and the number of cookies per domain
or in total.
The recommended cookie expiry upper limit is 400 days. User agents
may set a lower limit to enforce shorter data retention timelines, or
set the limit higher to support longer retention when appropriate
(e.g., server-to-server communication over HTTPS).
The goal of a restrictive cookie policy is often to improve security
or privacy. User agents often allow users to change the cookie
policy (see Section 7.3).
7.3. User Controls
User agents SHOULD provide users with a mechanism for managing the
cookies stored in the cookie store. For example, a user agent might
let users delete all cookies received during a specified time period
or all the cookies related to a particular domain. In addition, many
user agents include a user interface element that lets users examine
the cookies stored in their cookie store.
User agents SHOULD provide users with a mechanism for disabling
cookies. When cookies are disabled, the user agent MUST NOT include
a Cookie header field in outbound HTTP requests and the user agent
MUST NOT process Set-Cookie header fields in inbound HTTP responses.
User agents MAY offer a way to change the cookie policy (see
Section 7.2).
User agents MAY provide users the option of preventing persistent
storage of cookies across sessions. When configured thusly, user
agents MUST treat all received cookies as if the persistent-flag were
set to false. Some popular user agents expose this functionality via
"private browsing" mode [Aggarwal2010].
7.4. Expiration Dates
Although servers can set the expiration date for cookies to the
distant future, most user agents do not actually retain cookies for
multiple decades. Rather than choosing gratuitously long expiration
periods, servers SHOULD promote user privacy by selecting reasonable
cookie expiration periods based on the purpose of the cookie. For
example, a typical session identifier might reasonably be set to
expire in two weeks.
Bingler, et al. Expires 18 September 2025 [Page 46]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
8. Security Considerations
8.1. Overview
Cookies have a number of security pitfalls. This section overviews a
few of the more salient issues.
In particular, cookies encourage developers to rely on ambient
authority for authentication, often becoming vulnerable to attacks
such as cross-site request forgery [CSRF]. Also, when storing
session identifiers in cookies, developers often create session
fixation vulnerabilities.
Transport-layer encryption, such as that employed in HTTPS, is
insufficient to prevent a network attacker from obtaining or altering
a victim's cookies because the cookie protocol itself has various
vulnerabilities (see "Weak Confidentiality" and "Weak Integrity",
below). In addition, by default, cookies do not provide
confidentiality or integrity from network attackers, even when used
in conjunction with HTTPS.
8.2. Ambient Authority
A server that uses cookies to authenticate users can suffer security
vulnerabilities because some user agents let remote parties issue
HTTP requests from the user agent (e.g., via HTTP redirects or HTML
forms). When issuing those requests, user agents attach cookies even
if the remote party does not know the contents of the cookies,
potentially letting the remote party exercise authority at an unwary
server.
Although this security concern goes by a number of names (e.g.,
cross-site request forgery, confused deputy), the issue stems from
cookies being a form of ambient authority. Cookies encourage server
operators to separate designation (in the form of URLs) from
authorization (in the form of cookies). Consequently, the user agent
might supply the authorization for a resource designated by the
attacker, possibly causing the server or its clients to undertake
actions designated by the attacker as though they were authorized by
the user.
Instead of using cookies for authorization, server operators might
wish to consider entangling designation and authorization by treating
URLs as capabilities. Instead of storing secrets in cookies, this
approach stores secrets in URLs, requiring the remote entity to
supply the secret itself. Although this approach is not a panacea,
judicious application of these principles can lead to more robust
security.
Bingler, et al. Expires 18 September 2025 [Page 47]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
8.3. Clear Text
Unless sent over a secure channel (such as TLS [TLS13]), the
information in the Cookie and Set-Cookie header fields is transmitted
in the clear.
1. All sensitive information conveyed in these header fields is
exposed to an eavesdropper.
2. A malicious intermediary could alter the header fields as they
travel in either direction, with unpredictable results.
3. A malicious client could alter the Cookie header fields before
transmission, with unpredictable results.
Servers SHOULD encrypt and sign the contents of cookies (using
whatever format the server desires) when transmitting them to the
user agent (even when sending the cookies over a secure channel).
However, encrypting and signing cookie contents does not prevent an
attacker from transplanting a cookie from one user agent to another
or from replaying the cookie at a later time.
In addition to encrypting and signing the contents of every cookie,
servers that require a higher level of security SHOULD use the Cookie
and Set-Cookie header fields only over a secure channel. When using
cookies over a secure channel, servers SHOULD set the Secure
attribute (see Section 4.1.2.5) for every cookie. If a server does
not set the Secure attribute, the protection provided by the secure
channel will be largely moot.
For example, consider a webmail server that stores a session
identifier in a cookie and is typically accessed over HTTPS. If the
server does not set the Secure attribute on its cookies, an active
network attacker can intercept any outbound HTTP request from the
user agent and redirect that request to the webmail server over HTTP.
Even if the webmail server is not listening for HTTP connections, the
user agent will still include cookies in the request. The active
network attacker can intercept these cookies, replay them against the
server, and learn the contents of the user's email. If, instead, the
server had set the Secure attribute on its cookies, the user agent
would not have included the cookies in the clear-text request.
Bingler, et al. Expires 18 September 2025 [Page 48]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
8.4. Session Identifiers
Instead of storing session information directly in a cookie (where it
might be exposed to or replayed by an attacker), servers commonly
store a nonce (or "session identifier") in a cookie. When the server
receives an HTTP request with a nonce, the server can look up state
information associated with the cookie using the nonce as a key.
Using session identifier cookies limits the damage an attacker can
cause if the attacker learns the contents of a cookie because the
nonce is useful only for interacting with the server (unlike non-
nonce cookie content, which might itself be sensitive). Furthermore,
using a single nonce prevents an attacker from "splicing" together
cookie content from two interactions with the server, which could
cause the server to behave unexpectedly.
Using session identifiers is not without risk. For example, the
server SHOULD take care to avoid "session fixation" vulnerabilities.
A session fixation attack proceeds in three steps. First, the
attacker transplants a session identifier from his or her user agent
to the victim's user agent. Second, the victim uses that session
identifier to interact with the server, possibly imbuing the session
identifier with the user's credentials or confidential information.
Third, the attacker uses the session identifier to interact with
server directly, possibly obtaining the user's authority or
confidential information.
8.5. Weak Confidentiality
Cookies do not provide isolation by port. If a cookie is readable by
a service running on one port, the cookie is also readable by a
service running on another port of the same server. If a cookie is
writable by a service on one port, the cookie is also writable by a
service running on another port of the same server. For this reason,
servers SHOULD NOT both run mutually distrusting services on
different ports of the same host and use cookies to store security-
sensitive information.
Cookies do not provide isolation by scheme. Although most commonly
used with the http and https schemes, the cookies for a given host
might also be available to other schemes, such as ftp and gopher.
Although this lack of isolation by scheme is most apparent in non-
HTTP APIs that permit access to cookies (e.g., HTML's document.cookie
API), the lack of isolation by scheme is actually present in
requirements for processing cookies themselves (e.g., consider
retrieving a URI with the gopher scheme via HTTP).
Bingler, et al. Expires 18 September 2025 [Page 49]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
Cookies do not always provide isolation by path. Although the
network-level protocol does not send cookies stored for one path to
another, some user agents expose cookies via non-HTTP APIs, such as
HTML's document.cookie API. Because some of these user agents (e.g.,
web browsers) do not isolate resources received from different paths,
a resource retrieved from one path might be able to access cookies
stored for another path.
8.6. Weak Integrity
Cookies do not provide integrity guarantees for sibling domains (and
their subdomains). For example, consider foo.site.example and
bar.site.example. The foo.site.example server can set a cookie with
a Domain attribute of "site.example" (possibly overwriting an
existing "site.example" cookie set by bar.site.example), and the user
agent will include that cookie in HTTP requests to bar.site.example.
In the worst case, bar.site.example will be unable to distinguish
this cookie from a cookie it set itself. The foo.site.example server
might be able to leverage this ability to mount an attack against
bar.site.example.
Even though the Set-Cookie header field supports the Path attribute,
the Path attribute does not provide any integrity protection because
the user agent will accept an arbitrary Path attribute in a Set-
Cookie header field. For example, an HTTP response to a request for
http://site.example/foo/bar can set a cookie with a Path attribute of
"/qux". Consequently, servers SHOULD NOT both run mutually
distrusting services on different paths of the same host and use
cookies to store security-sensitive information.
An active network attacker can also inject cookies into the Cookie
header field sent to https://site.example/ by impersonating a
response from http://site.example/ and injecting a Set-Cookie header
field. The HTTPS server at site.example will be unable to
distinguish these cookies from cookies that it set itself in an HTTPS
response. An active network attacker might be able to leverage this
ability to mount an attack against site.example even if site.example
uses HTTPS exclusively.
Servers can partially mitigate these attacks by encrypting and
signing the contents of their cookies, or by naming the cookie with
the __Secure- prefix. However, using cryptography does not mitigate
the issue completely because an attacker can replay a cookie he or
she received from the authentic site.example server in the user's
session, with unpredictable results.
Bingler, et al. Expires 18 September 2025 [Page 50]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
Finally, an attacker might be able to force the user agent to delete
cookies by storing a large number of cookies. Once the user agent
reaches its storage limit, the user agent will be forced to evict
some cookies. Servers SHOULD NOT rely upon user agents retaining
cookies.
8.7. Reliance on DNS
Cookies rely upon the Domain Name System (DNS) for security. If the
DNS is partially or fully compromised, the cookie protocol might fail
to provide the security properties required by applications.
8.8. SameSite Cookies
8.8.1. Defense in depth
"SameSite" cookies offer a robust defense against CSRF attack when
deployed in strict mode, and when supported by the client. It is,
however, prudent to ensure that this designation is not the extent of
a site's defense against CSRF, as same-site navigations and
submissions can certainly be executed in conjunction with other
attack vectors such as cross-site scripting or abuse of page
redirections.
Understanding how and when a request is considered same-site is also
important in order to properly design a site for SameSite cookies.
For example, if a cross-site top-level request is made to a sensitive
page that request will be considered cross-site and SameSite=Strict
cookies won't be sent; that page's sub-resources requests, however,
are same-site and would receive SameSite=Strict cookies. Sites can
avoid inadvertently allowing access to these sub-resources by
returning an error for the initial page request if it doesn't include
the appropriate cookies.
Developers are strongly encouraged to deploy the usual server-side
defenses (CSRF tokens, ensuring that "safe" HTTP methods are
idempotent, etc) to mitigate the risk more fully.
Additionally, client-side techniques such as those described in
[app-isolation] may also prove effective against CSRF, and are
certainly worth exploring in combination with "SameSite" cookies.
Bingler, et al. Expires 18 September 2025 [Page 51]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
8.8.2. Top-level Navigations
Setting the SameSite attribute in "strict" mode provides robust
defense in depth against CSRF attacks, but has the potential to
confuse users unless sites' developers carefully ensure that their
cookie-based session management systems deal reasonably well with
top-level navigations.
Consider the scenario in which a user reads their email at MegaCorp
Inc's webmail provider https://site.example/. They might expect that
clicking on an emailed link to https://projects.example/secret/
project would show them the secret project that they're authorized to
see, but if https://projects.example has marked their session cookies
as SameSite=Strict, then this cross-site navigation won't send them
along with the request. https://projects.example will render a 404
error to avoid leaking secret information, and the user will be quite
confused.
Developers can avoid this confusion by adopting a session management
system that relies on not one, but two cookies: one conceptually
granting "read" access, another granting "write" access. The latter
could be marked as SameSite=Strict, and its absence would prompt a
reauthentication step before executing any non-idempotent action.
The former could be marked as SameSite=Lax, in order to allow users
access to data via top-level navigation, or SameSite=None, to permit
access in all contexts (including cross-site embedded contexts).
8.8.3. Mashups and Widgets
The Lax and Strict values for the SameSite attribute are
inappropriate for some important use-cases. In particular, note that
content intended for embedding in cross-site contexts (social
networking widgets or commenting services, for instance) will not
have access to same-site cookies. Cookies which are required in
these situations should be marked with SameSite=None to allow access
in cross-site contexts.
Likewise, some forms of Single-Sign-On might require cookie-based
authentication in a cross-site context; these mechanisms will not
function as intended with same-site cookies and will also require
SameSite=None.
Bingler, et al. Expires 18 September 2025 [Page 52]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
8.8.4. Server-controlled
SameSite cookies in and of themselves don't do anything to address
the general privacy concerns outlined in Section 7.1 of [RFC6265].
The "SameSite" attribute is set by the server, and serves to mitigate
the risk of certain kinds of attacks that the server is worried
about. The user is not involved in this decision. Moreover, a
number of side-channels exist which could allow a server to link
distinct requests even in the absence of cookies (for example,
connection and/or socket pooling between same-site and cross-site
requests).
8.8.5. Reload navigations
Requests issued for reloads triggered through user interface elements
(such as a refresh button on a toolbar) are same-site only if the
reloaded document was originally navigated to via a same-site
request. This differs from the handling of other reload navigations,
which are always same-site if top-level, since the source navigable's
active document is precisely the document being reloaded.
This special handling of reloads triggered through a user interface
element avoids sending SameSite cookies on user-initiated reloads if
they were withheld on the original navigation (i.e., if the initial
navigation were cross-site). If the reload navigation were instead
considered same-site, and sent all the initially withheld SameSite
cookies, the security benefits of withholding the cookies in the
first place would be nullified. This is especially important given
that the absence of SameSite cookies withheld on a cross-site
navigation request may lead to visible site breakage, prompting the
user to trigger a reload.
For example, suppose the user clicks on a link from
https://attacker.example/ to https://victim.example/. This is a
cross-site request, so SameSite=Strict cookies are withheld. Suppose
this causes https://victim.example/ to appear broken, because the
site only displays its sensitive content if a particular SameSite
cookie is present in the request. The user, frustrated by the
unexpectedly broken site, presses refresh on their browser's toolbar.
To now consider the reload request same-site and send the initially
withheld SameSite cookie would defeat the purpose of withholding it
in the first place, as the reload navigation triggered through the
user interface may replay the original (potentially malicious)
request. Thus, the reload request should be considered cross-site,
like the request that initially navigated to the page.
Bingler, et al. Expires 18 September 2025 [Page 53]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
Because requests issued for, non-user initiated, reloads attach all
SameSite cookies, developers should be careful and thoughtful about
when to initiate a reload in order to avoid a CSRF attack. For
example, the page could only initiate a reload if a CSRF token is
present on the initial request.
8.8.6. Top-level requests with "unsafe" methods
The "Lax" enforcement mode described in Section 5.6.7.1 allows a
cookie to be sent with a cross-site HTTP request if and only if it is
a top-level navigation with a "safe" HTTP method. Implementation
experience shows that this is difficult to apply as the default
behavior, as some sites may rely on cookies not explicitly specifying
a SameSite attribute being included on top-level cross-site requests
with "unsafe" HTTP methods (as was the case prior to the introduction
of the SameSite attribute).
For example, the concluding step of a login flow may involve a cross-
site top-level POST request to an endpoint; this endpoint expects a
recently created cookie containing transactional state information,
necessary to securely complete the login. For such a cookie, "Lax"
enforcement is not appropriate, as it would cause the cookie to be
excluded due to the unsafe HTTP request method, resulting in an
unrecoverable failure of the whole login flow.
The "Lax-allowing-unsafe" enforcement mode described in
Section 5.6.7.2 retains some of the protections of "Lax" enforcement
(as compared to "None") while still allowing recently created cookies
to be sent cross-site with unsafe top-level requests.
As a more permissive variant of "Lax" mode, "Lax-allowing-unsafe"
mode necessarily provides fewer protections against CSRF.
Ultimately, the provision of such an enforcement mode should be seen
as a temporary, transitional measure to ease adoption of "Lax"
enforcement by default.
9. IANA Considerations
9.1. Cookie
The HTTP Field Name Registry (see [HttpFieldNameRegistry]) needs to
be updated with the following registration:
Header field name: Cookie
Applicable protocol: http
Status: standard
Bingler, et al. Expires 18 September 2025 [Page 54]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
Author/Change controller: IETF
Specification document: this specification (Section 5.8.1)
9.2. Set-Cookie
The permanent message header field registry (see
[HttpFieldNameRegistry]) needs to be updated with the following
registration:
Header field name: Set-Cookie
Applicable protocol: http
Status: standard
Author/Change controller: IETF
Specification document: this specification (Section 5.6)
9.3. "Cookie Attributes" Registry
IANA is requested to create the "Cookie Attributes" registry,
defining the name space of attributes used to control cookies'
behavior. The registry should be maintained in a new registry group
called "Hypertext Transfer Protocol (HTTP) Cookie Attributes" at
https://www.iana.org/assignments/cookie-attribute-names
(https://www.iana.org/assignments/cookie-attribute-names).
9.3.1. Procedure
Each registered attribute name is associated with a description, and
a reference detailing how the attribute is to be processed and
stored.
New registrations happen on a "RFC Required" basis (see Section 4.7
of [RFC8126]). The attribute to be registered MUST match the
extension-av syntax defined in Section 4.1.1. Note that attribute
names are generally defined in CamelCase, but technically accepted
case-insensitively.
9.3.2. Registration
The "Cookie Attributes" registry should be created with the
registrations below:
Bingler, et al. Expires 18 September 2025 [Page 55]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
+==========+==================================+
| Name | Reference |
+==========+==================================+
| Domain | Section 4.1.2.3 of this document |
+----------+----------------------------------+
| Expires | Section 4.1.2.1 of this document |
+----------+----------------------------------+
| HttpOnly | Section 4.1.2.6 of this document |
+----------+----------------------------------+
| Max-Age | Section 4.1.2.2 of this document |
+----------+----------------------------------+
| Path | Section 4.1.2.4 of this document |
+----------+----------------------------------+
| SameSite | Section 4.1.2.7 of this document |
+----------+----------------------------------+
| Secure | Section 4.1.2.5 of this document |
+----------+----------------------------------+
Table 1
10. References
10.1. Normative References
[DOM-DOCUMENT-COOKIE]
WHATWG, "HTML - Living Standard", 18 May 2021,
<https://html.spec.whatwg.org/#dom-document-cookie>.
[FETCH] van Kesteren, A., "Fetch", n.d.,
<https://fetch.spec.whatwg.org/>.
[HTML] Hickson, I., Pieters, S., van Kesteren, A., Jägenstedt,
P., and D. Denicola, "HTML", n.d.,
<https://html.spec.whatwg.org/>.
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/rfc/rfc1034>.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
DOI 10.17487/RFC1123, October 1989,
<https://www.rfc-editor.org/rfc/rfc1123>.
Bingler, et al. Expires 18 September 2025 [Page 56]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet
Application Protocol Collation Registry", RFC 4790,
DOI 10.17487/RFC4790, March 2007,
<https://www.rfc-editor.org/rfc/rfc4790>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/rfc/rfc5234>.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010,
<https://www.rfc-editor.org/rfc/rfc5890>.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011,
<https://www.rfc-editor.org/rfc/rfc6454>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[SAMESITE] WHATWG, "HTML - Living Standard", 26 January 2021,
<https://html.spec.whatwg.org/#same-site>.
[USASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
10.2. Informative References
[Aggarwal2010]
Aggarwal, G., Burzstein, E., Jackson, C., and D. Boneh,
"An Analysis of Private Browsing Modes in Modern
Browsers", 2010,
<http://www.usenix.org/events/sec10/tech/full_papers/
Aggarwal.pdf>.
Bingler, et al. Expires 18 September 2025 [Page 57]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
[app-isolation]
Chen, E., Bau, J., Reis, C., Barth, A., and C. Jackson,
"App Isolation - Get the Security of Multiple Browsers
with Just One", 2011,
<http://www.collinjackson.com/research/papers/
appisolation.pdf>.
[CSRF] Barth, A., Jackson, C., and J. Mitchell, "Robust Defenses
for Cross-Site Request Forgery",
DOI 10.1145/1455770.1455782, ISBN 978-1-59593-810-7,
ACM CCS '08: Proceedings of the 15th ACM conference on
Computer and communications security (pages 75-88),
October 2008,
<http://portal.acm.org/citation.cfm?id=1455770.1455782>.
[HttpFieldNameRegistry]
"Hypertext Transfer Protocol (HTTP) Field Name Registry",
n.d., <https://www.iana.org/assignments/http-fields/>.
[prerendering]
Bentzel, C., "Chrome Prerendering", n.d.,
<https://www.chromium.org/developers/design-documents/
prerender>.
[PSL] "Public Suffix List", n.d.,
<https://publicsuffix.org/list/>.
[RFC2109] Kristol, D. and L. Montulli, "HTTP State Management
Mechanism", RFC 2109, DOI 10.17487/RFC2109, February 1997,
<https://www.rfc-editor.org/rfc/rfc2109>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/rfc/rfc4648>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/rfc/rfc6265>.
[RFC7034] Ross, D. and T. Gondrom, "HTTP Header Field X-Frame-
Options", RFC 7034, DOI 10.17487/RFC7034, October 2013,
<https://www.rfc-editor.org/rfc/rfc7034>.
Bingler, et al. Expires 18 September 2025 [Page 58]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
[RFC9113] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113,
DOI 10.17487/RFC9113, June 2022,
<https://www.rfc-editor.org/rfc/rfc9113>.
[RFC9114] Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114,
June 2022, <https://www.rfc-editor.org/rfc/rfc9114>.
[SERVICE-WORKERS]
Archibald, J. and M. Kruisselbrink, "Service Workers",
n.d., <https://www.w3.org/TR/service-workers/>.
[TLS13] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
Appendix A. Changes from RFC 6265
* Adds the same-site concept and the SameSite attribute.
(Section 5.2 and Section 4.1.2.7)
* Introduces cookie prefixes and prohibits nameless cookies from
setting a value that would mimic a cookie prefix. (Section 4.1.3
and Section 5.7)
* Prohibits non-secure origins from setting cookies with a Secure
flag or overwriting cookies with this flag. (Section 5.7)
* Limits maximum cookie size. (Section 5.7)
* Limits maximum values for max-age and expire. (Section 5.6.1 and
Section 5.6.2)
* Includes the host-only-flag as part of a cookie's uniqueness
computation. (Section 5.7)
* Considers potentially trustworthy origins as "secure".
(Section 5.7)
* Improves cookie syntax
- Treats Set-Cookie: token as creating the cookie ("", "token").
(Section 5.6)
- Rejects cookies without a name nor value. (Section 5.7)
- Specifies how to serialize a nameless/valueless cookie.
(Section 5.8.3)
Bingler, et al. Expires 18 September 2025 [Page 59]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
- Adjusts ABNF for cookie-pair and the Cookie header production
to allow for spaces. (Section 4.1.1)
- Explicitly handle control characters. (Section 5.6 and
Section 5.7)
- Specifies how to handle empty domain attributes. (Section 5.7)
- Requires ASCII characters for the domain attribute.
(Section 5.7)
* Refactors cookie retrieval algorithm to support non-HTTP APIs.
(Section 5.8.2)
* Specifies that the Set-Cookie line should not be decoded.
(Section 5.6)
* Adds an advisory section to assist implementers in deciding which
requirements to implement. (Section 3.2)
* Advises against sending invalid cookies due to public suffix list
changes. (Section 5.8.3)
* Removes the single cookie header requirement. (Section 5.8.1)
* Address errata 3444 by updating the path-value andextension-av
grammar, errata 4148 by updating the day-of-month, year, and time
grammar, and errata 3663 by adding the requested note.
(Section 4.1 and Section 5.1.4)
Acknowledgements
RFC 6265 was written by Adam Barth. This document is an update of
RFC 6265, adding features and aligning the specification with the
reality of today's deployments. Here, we're standing upon the
shoulders of a giant since the majority of the text is still Adam's.
Thank you to both Lily Chen and Steven Englehardt, editors emeritus,
for their significant contributions improving this draft.
Authors' Addresses
Steven Bingler (editor)
Google LLC
Email: bingler@google.com
Bingler, et al. Expires 18 September 2025 [Page 60]
Internet-Draft Cookies: HTTP State Management Mechanism March 2025
Mike West (editor)
Google LLC
Email: mkwst@google.com
URI: https://mikewest.org/
John Wilander (editor)
Apple, Inc
Email: wilander@apple.com
Bingler, et al. Expires 18 September 2025 [Page 61]