[ GLSA 200403-11 ] Squid ACL [url_regex] bypass vulnerability

From: Kurt Lieber (klieber_at_gentoo.org)
Date: 03/31/04

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    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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