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                              CERT-Renater

                 Note d'Information No. 2016/VULN075
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DATE                : 25/02/2016

HARDWARE PLATFORM(S): /

OPERATING SYSTEM(S): Systems running Squid versions 3.x, 4.x prior to
                                  3.5.15, 4.0.7.

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http://www.squid-cache.org/Advisories/SQUID-2016_2.txt
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Squid Proxy Cache Security Update Advisory SQUID-2016:2
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Advisory ID:        SQUID-2016:1
Date:               February 23, 2016
Summary:            Multiple Denial of Service issues
                      in HTTP Response processing
Affected versions:  Squid 3.x -> 3.5.16
                      Squid 4.x -> 4.0.7
Fixed in version:   Squid 4.0.7, 3.5.15
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      http://www.squid-cache.org/Advisories/SQUID-2016_2.txt
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Problem Description:

   Due to incorrect bounds checking Squid is vulnerable to a denial
   of service attack when processing HTTP responses.

   Due to incorrect error handling Squid-4 is vulnerable to a denial
   of service attack when processing malformed HTTP responses.

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Severity:

   These problems allow remote servers delivering certain unusual
   HTTP response syntax to trigger a denial of service for all
   clients accessing the Squid service.

   HTTP responses containing malformed headers that trigger this
   issue are becoming common. We are not certain at this time if
   that is a sign of malware or just broken server scripting.

   Details of a trivial attack are already circulating publicly.

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Updated Packages:

   These bugs are fixed by Squid version 3.5.15 and 4.0.7.

   In addition, patches addressing these problems for the stable
   release can be found in our patch archives:

Squid 3.5:
 
http://www.squid-cache.org/Versions/v3/3.5/changesets/squid-3.5-13990.patch
 
http://www.squid-cache.org/Versions/v3/3.5/changesets/squid-3.5-13991.patch

   If you are using a prepackaged version of Squid then please refer
   to the package vendor for availability information on updated
   packages.

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Determining if your version is vulnerable:

   All Squid-3.2 and older have not been tested but are expected to
   be vulnerable.

   All unpatched Squid-3.3 versions are vulnerable.

   All unpatched Squid-3.4 versions are vulnerable.

   All unpatched Squid-3.5.14 and older are vulnerable.

   All unpatched Squid-4.0.6 and older are vulnerable.

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Workaround:

   There are no good workarounds known for these vulnerabilities.

   The following squid.conf settings can protect Squid-3.5 (only)
   against the publicly published attack. But unpatched Squid
   remain vulnerable to other known attacks:

     acl Vary rep_header Vary .
     store_miss deny Vary

Or,

   The following squid.conf settings can protect against the
   publicly published attack. But unpatched Squid remain vulnerable
   to other known attacks:

     cache deny all

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Contact details for the Squid project:

   For installation / upgrade support on binary packaged versions
   of Squid: Your first point of contact should be your binary
   package vendor.

   If your install and build Squid from the original Squid sources
   then the squid-users@lists.squid-cache.org mailing list is your
   primary support point. For subscription details see
   <http://www.squid-cache.org/Support/mailing-lists.html>.

   For reporting of non-security bugs in the latest STABLE release
   the squid bugzilla database should be used
   <http://bugs.squid-cache.org/>.

   For reporting of security sensitive bugs send an email to the
   squid-bugs@lists.squid-cache.org mailing list. It's a closed
   list (though anyone can post) and security related bug reports
   are treated in confidence until the impact has been established.

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Credits:

   The bounds checking vulnerability was identified and reported by
   Mathias Fischer from Open Systems AG.

   The bounds checking vulnerability was fixed by Alex Rousskov from
   The Measurement Factory.

   The error handling vulnerability was found and fixed by Alex
   Rousskov from The Measurement Factory.

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Revision history:

   2016-02-17 06:51:25 UTC Initial Report
   2016-02-18 04:15:33 UTC Patches Released
   2016-02-19 23:15:41 UTC Additional Patches Released
   2016-02-23 16:37:27 UTC Attack PoC becomes public knowledge
   2016-02-23 18:23:00 UTC Packages Released
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