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Gentoo: squid Access control escape vulnerability Print E-mail
User Rating:      How can I rate this item?
Posted by LinuxSecurity.com Team   
Gentoo A URL can be specially crafted to automatically bypass the squid Access Control functionality.

Gentoo Linux Security Advisory                           GLSA 200403-11
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                                              http://security.gentoo.org
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  Severity: Normal
     Title: Squid ACL [url_regex] bypass vulnerability
      Date: March 30, 2004
      Bugs: #45273
        ID: 200403-11

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Synopsis
========

Squid versions 2.0 through to 2.5.STABLE4 could allow a remote attacker
to bypass Access Control Lists by sending a specially-crafted URL
request containing '%00': in such circumstances; the url_regex ACL may
not properly detect the malicious URL, allowing the attacker to
effectively bypass the ACL.

Background
==========

Squid is a fully-featured Web Proxy Cache designed to run on Unix
systems that supports proxying and caching of HTTP, FTP, and other
URLs, as well as SSL support, cache hierarchies, transparent caching,
access control lists and many other features.

Affected packages
=================

    -------------------------------------------------------------------
     Package        /   Vulnerable   /                      Unaffected
    -------------------------------------------------------------------
     net-www/squid        < 2.5.5                             >= 2.5.5

Description
===========

A bug in Squid allows users to bypass certain access controls by
passing a URL containing "%00" which exploits the Squid decoding
function. This may insert a NUL character into decoded URLs, which may
allow users to bypass url_regex access control lists that are enforced
upon them.

In such a scenario, Squid will insert a NUL character after the"%00"
and it will make a comparison between the URL to the end of the NUL
character rather than the contents after it: the comparison does not
result in a match, and the user's request is not denied.

Impact
======

Restricted users may be able to bypass url_regex access control lists
that are enforced upon them which may cause unwanted network traffic as
well as a route for other possible exploits. Users of Squid 2.5STABLE4
and below who require the url_regex features are recommended to upgrade
to 2.5STABLE5 to maintain the security of their infrastructure.

Workaround
==========

A workaround is not currently known for this issue. All users are
advised to upgrade to the latest version of Squid.

Resolution
==========

Squid can be updated as follows:

    # emerge sync

    # emerge -pv ">=net-www/squid-2.5.5"
    # emerge ">=net-www/squid-2.5.5"

References
==========

  [ 1 ]  http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0189
  [ 2 ]  http://www.squid-cache.org/Advisories/SQUID-2004_1.txt

Concerns?
=========

Security is a primary focus of Gentoo Linux and ensuring the
confidentiality and security of our users machines is of utmost
importance to us. Any security concerns should be addressed to
security@gentoo.org or alternatively, you may file a bug at 
http://bugs.gentoo.org.

 
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