Happy Eyeballs Considerations for HTTP State Management Mechanisms
draft-vyncke-v6ops-happy-eyeballs-cookie-00
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Éric Vyncke | ||
| Last updated | 2014-10-27 | ||
| Stream | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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draft-vyncke-v6ops-happy-eyeballs-cookie-00
IPv6 Operations E. Vyncke
Internet-Draft Cisco
Intended status: Informational October 27, 2014
Expires: April 30, 2015
Happy Eyeballs Considerations for HTTP State Management Mechanisms
draft-vyncke-v6ops-happy-eyeballs-cookie-00
Abstract
HTTP servers usually save session states in their persistent storage
indexed by session cookies generated by the HTTP servers. It is up
to the HTTP user-agent to send this session cookie on each HTTP
request. Some HTTP servers check whether the cookie is associated
with the HTTP user-agent by the means of the user-agent IP address...
If the Happy Eyeball mechanism is used to select between IPv6 and
IPv4, it may happen that while using the same HTTP server, some HTTP
requests are done over IPv6 and the others over IPv4, which leads to
two different sets of session states in the HTTP server. This has
the consequence of inconsistencies at the HTTP server.
The only purpose of this document is to document this issue.
A similar problem arises with the use of non RFC 6888 compliant Large
Scale NAT (LSN) devices used to access an IPv4-only HTTP server.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 30, 2015.
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Copyright Notice
Copyright (c) 2014 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
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Table of Contents
1. HTTP Session Management with HTTP Cookie . . . . . . . . . . 2
2. Other Use of Session Cookies . . . . . . . . . . . . . . . . 3
3. Happy Eyeballs Issue . . . . . . . . . . . . . . . . . . . . 3
4. Large Scale NAT Issue . . . . . . . . . . . . . . . . . . . . 4
5. Potential Mitgation . . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
9. Informative References . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. HTTP Session Management with HTTP Cookie
HTTP requests are basically stateless, therefore if a HTTP server
requires to have some states associated to a HTTP user-agent (such as
user name, login state, history, shopping basket, ...), there is a
need to conserve those states. This is usually done by using a HTTP
cookie (see also [RFC6265]) identifying the session; also called
"session state cookie".
This session state cookie is generated by the HTTP server at the very
first HTTP request from a HTTP user-agent. The cookie is usually
opaque (often a random number) and has no semantic except as being an
index within the persistent storage of the HTTP server. This index
is used to access the complete state of the user-agent. This
mechanism is secure if the cookie is transferred with confidentiality
between the server and the user-agent. If the cookie transfer and
storage are not secured, then any hostile user-agent can reuse this
cookie to access the full original session states (including shopping
basket, payment details, ...).
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Some HTTP applications link the user-agent IP address (whether IPv6
or IPv4) to the session state, probably for additional security
checks in order to prevent session cookie stealing. This link leads
to some issues in a dual-stack world which are described in this
document.
The author knows about at least two large web sites having this
problem. It was so severe that those sites which were dual-stack had
to move back to being IPv4-only... until the application and its
security is updated.
2. Other Use of Session Cookies
Beside the use of session cookies by the HTTP server to keep states
on the server, the very same cookie is also sometimes used by Server
Load Balancing (SLB) mechanism to ensure that all HTTP requests from
the same user-agent (even if behind a NAT) are always sent to the
same physical HTTP server. This is required if the server persistent
storage is local to the server and is not shared by all the physical
servers behind the SLB.
3. Happy Eyeballs Issue
When a HTTP user-agent uses the Happy Eyeball [RFC6555] mechanism to
access a HTTP server, then, part of the HTTP requests can happen over
IPv6 and another part over IPv4 if the latency between IPv4 and IPv6
varies quickly over time. If there is a link between the session
cookie and the user-agent IP address, then upon the first change of
IP protocol version, the states associated to the cookie will be
invalidated and will be deleted. Here is an example:
1. User-agent with IPv4 address, ADDR4, connect to the server by
using IPv4 because IPv6 is slower; the first request does not
have any HTTP cookie;
2. Server generates a new cookie C4 and stores in its persistent
storage that C4 is associated with address ADDR4;
3. User-agent continues his/her session using IPv4, on each new
request the HTTP server receives the cookie C4 and checks that
the user-agent address is indeed ADDR4;
4. Latency of IPv6 changes and becomes now faster than IPv4;
5. User-agent now uses its IPv6 address, ADDR6, to connect to the
same server and continues to use the same cookie C4 as the server
name is unchanged;
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6. The server receives the HTTP request with the C4 cookie and
checks whether C4 is associated with ADDR6 which is not the
case... All session states are deleted and a new cookie, C6, is
generated and associated to the IPV6 address ADDR6;
7. The end-user becomes frustrated because he/she has to restart
his/her complete session from the beginning.
This cookie invalidation may have some security benefit but it
actually prevents a host using Happy Eyeballs to have a persistent
session with a dual-stack HTTP server; with painful consequences for
the user-experience: disconnection, loss of shopping basket, ...
4. Large Scale NAT Issue
[RFC6888] describes the LSN requirements but not all LSN implement
them. Some LSN in the real world have a pool of IPv4 addresses and
do not always use the same public IPv4 address for all requests from
a LSN client. This obviously leads to the same problem as in section
Section 3. Whether the LSN is used by IPv4 clients or by IPv6
clients does not make any difference to the problem.
5. Potential Mitgation
A potential mitigation for this issue is NOT to link any HTTP state
management (including cookies) to any IP address of the HTTP user-
agent.
6. IANA Considerations
This document contains no IANA considerations.
7. Security Considerations
The association of the session cookie with the user-agent IP address
has some security value as it effectively prevents "session cookie
stealing"; this benefit should be balanced with the lack of
persistent session and the remaining vulnerability if the HTTP
session can be intercepted by a man-in-the-middle attack.
8. Acknowledgements
The author would like to thank Dan Wing and Andrew Yourtchenko for
some discussions on this topic.
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9. Informative References
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
April 2011.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, April 2012.
[RFC6888] Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
and H. Ashida, "Common Requirements for Carrier-Grade NATs
(CGNs)", BCP 127, RFC 6888, April 2013.
Author's Address
Eric Vyncke
Cisco
De Kleetlaan 6a
Diegem 1831
Belgium
Phone: +32 2 778 4677
Email: evyncke@cisco.com
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