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             AUSCERT External Security Bulletin Redistribution

          Squid Proxy Cache Security Update Advisory SQUID-2016:1
                             17 February 2016


        AusCERT Security Bulletin Summary

Product:           Squid
Publisher:         Squid
Operating System:  Windows
                   UNIX variants (UNIX, Linux, OSX)
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade

Original Bulletin: 

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Squid Proxy Cache Security Update Advisory SQUID-2016:1

Advisory ID:        SQUID-2016:1
Date:               February 16, 2016
Summary:            Remote Denial of Service issue
                    in SSL/TLS processing.
Affected versions:  Squid 3.5.13
                    Squid 4.0.4 -> 4.0.5
Fixed in version:   Squid 4.0.6, 3.5.14


Problem Description:

 Due to incorrectly handling server errors Squid is vulnerable to
 a denial of service attack when connecting to TLS or SSL servers.



 This problem allows any trusted client to perform a denial of
 service attack on the Squid service regardless of whether TLS or
 SSL is configured for use in the proxy.

 Misconfigured client or server software may trigger this issue
 to perform a denial of service unintentionally.

 However, the bug is exploitable only if Squid is built using the
 --with-openssl option.


Updated Packages:

 These bugs are fixed by Squid version 3.5.14 and 4.0.6.

 In addition, patches addressing this problem for stable releases
 can be found in our patch archives:

Squid 3.5:

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


Determining if your version is vulnerable:

 All Squid-3.4 and older versions are not vulnerable.

 All Squid-3.5.12 and older 3.5 versions are not vulnerable.

 All Squid-3.5 built without OpenSSL support are not vulnerable.

 All Squid-4.0.3 and older 4.0 versions are not vulnerable.

 All Squid-4 built without OpenSSL support are not vulnerable.

 All unpatched Squid-3.5.13, 4.0.4, and 4.0.5 built using
 --with-openssl are vulnerable.

 The following command can be used to easily determine if a
 vulnerable build is being used:
  squid -v



 Disabling service for https:// URLs entirely at the top of the
 squid.conf http_access rules fully protects against this

   acl HTTPS proto HTTPS
   http_access deny HTTPS


 Relaying outbound HTTPS traffic through a non-vulnerable proxy
 protects against the issue unless the SSL-bump splice feature is
 being used.


 Disabling service for irregular HTTPS ports protects against the
 simplest forms of attack while retaining most HTTPS service:

   acl HTTPS proto HTTPS
   http_access deny HTTPS !SSL_Ports


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

 For reporting of non-security bugs in the latest STABLE release
 the squid bugzilla database should be used

 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.



 The vulnerability was reported and fixed by Christos Tsantilas of
 The Measurement Factory.


Revision history:

 2016-02-12 17:50:38 GMT Initial Report
 2016-02-12 18:05:44 GMT Patch Released
 2016-02-15 17:15:00 GMT Packages Released

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