Squid before 3.5.6 does not properly handle CONNECT method peer responses when configured with cache_peer, which allows remote attackers to bypass intended restrictions and gain access to a backend proxy via a CONNECT request.
lists.fedoraproject.org/pipermail/package-announce/2016-May/183598.html
lists.opensuse.org/opensuse-security-announce/2016-08/msg00010.html
lists.opensuse.org/opensuse-security-announce/2016-08/msg00040.html
lists.opensuse.org/opensuse-updates/2016-08/msg00069.html
www.debian.org/security/2015/dsa-3327
www.openwall.com/lists/oss-security/2015/07/06/8
www.openwall.com/lists/oss-security/2015/07/09/12
www.openwall.com/lists/oss-security/2015/07/10/2
www.openwall.com/lists/oss-security/2015/07/17/14
www.securityfocus.com/bid/75553
www.securitytracker.com/id/1032873
www.squid-cache.org/Advisories/SQUID-2015_2.txt
www.squid-cache.org/Versions/v3/3.1/changesets/squid-3.1-10494.patch
www.squid-cache.org/Versions/v3/3.4/changesets/squid-3.4-13225.patch
www.squid-cache.org/Versions/v3/3.5/changesets/squid-3.5-13856.patch