Multiple Browser Cookie Injection Vulnerabilities
From Zone-H.org:
Quote:
09/17/2004
Westpoint Security Advisory
---------------------------
Title: Multiple Browser Cookie Injection Vulnerabilities
Risk Rating: Low
Software: Multiple Web Browsers
Platforms: Unix and Windows
Author: Paul Johnston <[email protected]>
assisted by Richard Moore <[email protected]>
Date: 15 September 2004
Advisory ID#: wp-04-0001
URL: http://www.westpoint.ltd.uk/advisories/wp-04-0001.txt
CVE: Multiple assigned, see main text
Overview
--------
A design goal for cookies is to "prevent the sharing of session
information between hosts that are in different domains." It appears
current implementations are successful at allowing a domain to keep its
cookies private. However, multiple mechanisms have been discovered for one
domain to inject cookies into another. These could be used to perform
session fixation attacks against web applications.
Recommendations:
* Affected browsers be patched for these vulnerabilities.
* Web applications implement application layer mitigations for session
fixation attacks, as described in [2].
Tested:
Internet Explorer 6.0 for Windows 2000, all patches
Konqueror 3.1.4 for SuSE 9.0
Mozilla Firefox 0.9.2 for Windows 2000
Opera 7.51 for Windows 2000
Cross-Domain Cookie Injection
-----------------------------
Vulnerable:
Konqueror CAN-2004-0746
Internet Explorer CAN-2004-0866
Mozilla CAN-2004-0867
Not vulnerable:
Opera
By default, cookies are only sent to the host that issued them. There is
an optional "domain" attribute that overrides this behaviour. For example,
red.example.com could set a cookie with domain=.example.com. This would
then be sent to any host in the .example.com domain.
There is potential for abuse here, consider the case where red.example.com
sets a cookie with domain=.com. In principle this would be sent to any
host in the .com domain. However [1] requires browsers to reject cookies
where:
"The value for the Domain attribute contains no embedded dots"
This prevents a cookie being set with domain=.com. However, this does not
extend to country domains that are split into two parts. For example,
red.example.co.uk could set a cookie with domain=.co.uk and this will be
sent to all hosts in the .co.uk domain. Mozilla follows the RFC exactly
and is vulnerable to this. Konqueror and Internet Explorer have some
further protection, preventing domains of the following forms:
* Where the 2nd level domain is two or fewer characters, i.e. xx.yy or
x.yy
* Domains of the form (com|net|mil|org|gov|edu|int).yy
This does prevent .co.uk cross domain cookie injection but does not
protect all domains. For example, the following .uk domains are
unprotected:
.ltd.uk
.plc.uk
.sch.uk
.nhs.uk
.police.uk
.mod.uk
When testing with Opera, it appeared that browser always correctly
detected the domain. It is not immediately clear how Opera does this
check.
Example exploitation:
1) http://example.ltd.uk/ is identified for attack. It uses the "sid"
cookie to hold the session ID.
2) Attacker obtains attacker.ltd.uk domain
3) User is enticed to click link to http://attacker.ltd.uk/
4) This site sets the "sid" cookie with domain=.ltd.uk
5) When user logs into example.ltd.uk, they are using a sesion ID known
to the attacker.
6) Attacker now has a logged-in session ID and has compromised the
user's account.
Exploitation is dependent on the user clicking an untrusted link. However,
it is fundamental to the use of the web that we do sometimes click
untrusted links. This attack can happen regardless of the use of SSL.
Cross Security Boundary Cookie Injection
----------------------------------------
Vulnerable:
Internet Explorer CAN-2004-0869
Konqueror CAN-2004-0870
Mozilla CAN-2004-0871
Opera CAN-2004-0872
By default cookies are sent to all ports on the host that issued them,
regardless of whether SSL is in use. There is an optional "secure"
attribute that restricts sending to secure channels. This prevents secure
cookies leaking out over insecure channels. However, there is no
protection to prevent cookies set over a non-secure channel being
presented on a secure channel. In general to maintain proper boundaries
between security levels, it is necessary to defend against both attacks -
protecting both confidentiality and integrity.
Example exploitation:
1) https://example.com/ identified for attack, which uses "sid" cookie
as session ID.
2) User is enticed to click link to http://example.com/
3) By some mechanism the attacker intercepts this request and sets the
"sid" cookie
4) When user logs into https://example.com/ they are using a sesion ID
known to the attacker.
5) Attacker now has a logged-in session ID and has compromised the
user's account.
In addition to the user clicking an untrusted link, exploitation is
dependent on the attacker tampering with non-SSL network traffic. This is
a reasonable assumption as the purpose of SSL is to provide security over
an insecure network.
References
----------
[1] RFC2965 - HTTP State Management Mechanism
http://www.ietf.org/rfc/rfc2965.txt
[2] Session Fixation Vulnerability in Web-based Applications
http://www.acros.si/papers/session_fixation.pdf
[3] Persistent Client State - HTTP Cookies
http://www.netscape.com/newsref/std/cookie_spec.html
[4] Cookies and Cookie Handling in Opera 7 Explained
http://o.bulport.com/index.php?item=55
