Internet DRAFT - draft-vyncke-v6ops-happy-eyeballs-cookie
draft-vyncke-v6ops-happy-eyeballs-cookie
IPv6 Operations E. Vyncke
Internet-Draft Cisco
Intended status: Informational March 6, 2015
Expires: September 7, 2015
HTTP State Management Mechanisms with Multiple Addresses User Agents
draft-vyncke-v6ops-happy-eyeballs-cookie-01
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.
Everything linking a state to an IP address (such as OAuth access
code) to an IP address has the same issue.
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 in more
details than in section 8.2 of RFC 6883 including security
considerations and mitigations.
A similar problem arises with the use of non RFC 6888 compliant
Carrier-Grade NAT (CGN) devices used to access an IPv4-only HTTP
server or HTTP user-agent using multi-homing.
Status of This Memo
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This Internet-Draft will expire on September 7, 2015.
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Table of Contents
1. HTTP Session Management with HTTP Cookie . . . . . . . . . . 2
1.1. Other Use of Session Cookies . . . . . . . . . . . . . . 3
1.2. new section . . . . . . . . . . . . . . . . . . . . . . . 3
2. Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Happy Eyeballs Issue . . . . . . . . . . . . . . . . . . 4
2.2. Carrier-Grade NAT Issue . . . . . . . . . . . . . . . . . 4
2.3. Multiple Interfaces Issue . . . . . . . . . . . . . . . . 5
3. Mitigations . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. Informative References . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
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 [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
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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, ...); this attack is called 'session cookie
stealing'. This attack can happen if the HTTP traffic is intercepted
by a man-in-the-middle attack but a good use of Transport Level
Security RFC5246 [RFC5246] can prevent it. The attack can also
happen with some hostile scripting or other pieces of malware running
on the user agent, that could copy and send the session cookie to the
hostile user-agent; hence, it is not enough to use TLS to secure the
session cookies.
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.
1.1. 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.
1.2. new section
Actually the problem is more generic than the session cookie,
everything linking a state to an IP address has the same issue. This
includes OAuth [RFC6749] access tokens, bearer tokens, ... but also
other mechanisms such as rate limiting per IP address or access
control per IP address (for instance a captive portal for a guest
net).
2. Issues
Similar issues can be caused by Happy Eyeball RFC6555 [RFC6555],
Carrier-Grade NAT (CGN) and having multiple interface or being multi-
homed.
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2.1. Happy Eyeballs Issue
When a HTTP user-agent uses the Happy Eyeball 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;
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, ...
2.2. Carrier-Grade NAT Issue
RFC6888 [RFC6888] describes the CGN requirements but not all CGN
implement them. Some CGN 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 CGN client. This obviously leads to the same problem
as in section Section 2.1. This will happen for IPv4-only HTTP
servers.
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Whether the CGN is used by IPv4 clients or by IPv6 clients (via NAT64
RFC6146 [RFC6146])does not make any difference to the problem. The
use of the address family translation by MAP-T MAP-T
[I-D.ietf-softwire-map-t] does not suffer from this issue for
IPv4-only HTTP servers since one subscriber is restricted to several
layer-4 ports from a single IPv4 address.
2.3. Multiple Interfaces Issue
When the HTTP user-agent has multiple interfaces, for example 3GPP
and Wi-Fi, the preferred IP address depends on the WiFi or 3GPP
availability. In this case, a similar issue to Section 2.1 also
happens as the session cookie can be linked first to the Wi-Fi IP
address then when the user-agent looses its Wi-Fi connectivity the
session cookie will be overwritten by a new session cookie linked to
the 3GPP address.
Whether the user-agent uses IPv4-only, IPv6-only or dual-stack has no
impact on the issue.
3. Mitigations
The obvious mitigation for this issue is NOT to link any HTTP state
management (including cookies) to any IP address of the HTTP user-
agent at the risk of increasing the risk of "session cookie
stealing".
The author also believes that:
Multipath TCP RFC6824 [RFC6824] hides completely the set of
addresses of the client to the application. Only the first
subflow's IP addresses are exposed to the application, even if a
later subflow uses a different address family; so, any session
cookie will be permanently linked to the first IP address used by
the HTTP user-agent;
HTTP/2 [I-D.ietf-httpbis-http2] multiplexes multiple HTTP sessions
over a single TCP connection, therefore, Happy Eyeball (or bad
CGN) sees only one TCP connection and a change of IP address will
never occur during the lifetime of this TCP connection.
4. IANA Considerations
This document contains no IANA considerations.
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5. Security Considerations
The association of the session cookie with the user-agent IP address
has some security value as it can help prevent "session cookie
stealing" in some limited situations; 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.
Moreover with more and more CGN being deployed, linked a session
cookie to an IP address shared by hundreds of subscribers is less
effective as the cookie could be reused by any subscribers using the
same shared public IP address.
6. Acknowledgements
The author would like to thank Brian Carpenter, Ray Hunter, Jeroen
Massar, Dan Metzler, Erik Nygren, Mark ZZZ Smith, Joe Touch, Dan Wing
and Andrew Yourtchenko for some discussions on this topic. Of
course, RFC6883 [RFC6883] has already mentionned this issue without
many details.
7. Informative References
[I-D.ietf-httpbis-http2]
Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer
Protocol version 2", draft-ietf-httpbis-http2-17 (work in
progress), February 2015.
[I-D.ietf-softwire-map-t]
Li, X., Bao, C., Dec, W., Troan, O., Matsushima, S., and
T. Murakami, "Mapping of Address and Port using
Translation (MAP-T)", draft-ietf-softwire-map-t-08 (work
in progress), December 2014.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[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.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
6749, October 2012.
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[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, January 2013.
[RFC6883] Carpenter, B. and S. Jiang, "IPv6 Guidance for Internet
Content Providers and Application Service Providers", RFC
6883, March 2013.
[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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