WEBSEC D. Ross
Internet-Draft Microsoft
Intended status: Standards Track T. Gondrom
Expires: September 8, 2011 March 7, 2011
HTTP Header Frame Options
draft-gondrom-frame-options-00
Abstract
To improve the protection of web applications against Cross Site
Request Forgery (CSRF) and Clickjacking this standards defines a http
response header that declares a policy communicated from a host to
the client browser whether the transmitted content MUST NOT be
displayed in frames of other pages from different origins or a list
of trusted origins which are allowed to frame the content.
Status of this Memo
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2. Frame-Options Header . . . . . . . . . . . . . . . . . . . . . 3
2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Backus-Naur Form (BNF) . . . . . . . . . . . . . . . . . . 4
2.3. Examples of Frame-Options Headers . . . . . . . . . . . . . 4
3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Registration Template . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . . 5
Appendix A. Description of a Clickjacking attack . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
In 2009 and 2010 many browser vendors introduced the use of a non-
standard http header RFC 2616 [RFC2616] "X-Frame-Options" to protect
against Clickjacking [Clickjacking] and Cross Site Request Forgery
(CSRF) [CSRF]. This standard is to replace the non-standard header.
With Clickjacking and CSRF an attacker tricks a user into clicking on
a button or link to another page and by thus executing an unintended
command in the context of a different web application. For example
with Clickjacking the attacker might use transparent or opaque layers
to integrate and obscure a button to another page so that the user
may click on it in the expectation of a different action. So, in
this way the attacker is "hijacking" the "Click" on a button meant by
the user to be sent to host A, while clicking the button in effect
sends a message to host B. If the user does for example also have an
open session with host B this can lead to a CSRF attack and executing
a command in the session context of the user (using the user's
authentication and authorization) on host B without his intention or
knowledge.
The by "Frame-Options" provided defense mechanism against
Clickjacking is to allow a secure web page from host B to declare
that its content (for example a button, links, text, etc.) must not
be displayed in a frame of another page (e.g. from host A). In
principle this is done by a policy declared in the HTTP header and
obeyed by conform browser implementations.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Frame-Options Header
The Frame-Options HTTP response header indicates a policy whether a
browser MUST NOT allow to render a page in a <frame> or <iframe> .
Hosts can declare this policy in the header of their HTTP responses
to prevent clickjacking attacks, by ensuring that their content is
not embedded into other pages or frames.
2.1. Syntax
The header field name is:
Frame-Options
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There are three different values for the header field. These values
are exclusive, that is NOT more than one of the three values MUST be
set.
DENY
A browser receiving content with this header MUST NOT display
this content in any frame.
SAMEORIGIN
A browser receiving content with this header MUST NOT display
this content in any frame from a page of different origin than
the content itself.
TRUSTED (followed by a list of URIs of trusted origins)
A browser receiving content with this header MUST NOT display
this content in any frame from a page of different origin than
any of the listed origins. This allows deployment with multi-
domain sites, as the webmaster can define a whitelist of
origins that are allowed to frame the page. While this can
expose the page to risks by the trusted origins, in some cases
it may be necessary to use content from other domains or more
than one origin (hostname).
2.2. Backus-Naur Form (BNF)
The RFC 822 [RFC0822] EBNF of the Frame-Options header is:
Frame-Options = "Frame-Options" ":" "DENY"/ "SAMEORIGIN" /
("TRUSTED" ":" Origin-List)
Origin-List = 1*URI
[TBD] with URI as defined in the websec-origin draft
[TBD] Or should we use the ABNF (RFC 2234) alternatively or in
addition?
2.3. Examples of Frame-Options Headers
3. Acknowledgements
This document was derived from input from specifications published by
various browser vendors like Microsoft (Eric Law, David Ross),
Mozilla, Google, Opera and Apple.
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4. IANA Considerations
This memo a request to IANA to include the specified HTTP header in
registry as outlined in Registration Procedures for Message Header
Fields [RFC3864]
4.1. Registration Template
PERMANENT MESSAGE HEADER FIELD REGISTRATION TEMPLATE:
Header field name: Frame-Option
Applicable protocol: http [RFC2616]
Status: Standard
Author/Change controller: IETF
Specification document(s): draft-gondrom-frame-options
Related information:
Figure 1
5. Security Considerations
The introduction of the http header FRAME-OPTIONS does improve the
protection against Clickjacking, however it is not self-sufficient on
its own but MUST be used in conjunction with other security measures
like secure coding and Content Security Policy (CSP)
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
6.2. Informative References
[CSRF] OWASP (Open Web Application Security Project), "OWASP
Top-10: Cross-Site Request Forgery (CSRF)", 2010,
<http://www.owasp.org/index.php/Top_10_2010-A5>.
[Clickjacking]
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OWASP (Open Web Application Security Project),
"Clickjacking", 2010,
<http://www.owasp.org/index.php/Clickjacking>.
[RFC0822] Crocker, D., "Standard for the format of ARPA Internet
text messages", STD 11, RFC 822, August 1982.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
Appendix A. Description of a Clickjacking attack
More detailed explanation of a Clickjacking attack
Authors' Addresses
David Ross
Microsoft
U.S.
Phone:
Email:
Tobias Gondrom
Kruegerstr. 5A
Unterschleissheim,
Germany
Phone: +44 7521003005
Email: tobias.gondrom@gondrom.org
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