The Mail Fetch plugin in SquirrelMail 1.4.20 and earlier allows remote authenticated users to bypass firewall restrictions and use SquirrelMail as a proxy to scan internal networks via a modified POP3 port number.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2010-1658
http://www.vupen.com/english/advisories/2010/1554
http://www.vupen.com/english/advisories/2010/1536
http://www.vupen.com/english/advisories/2010/1535
http://www.securityfocus.com/bid/40307
http://www.securityfocus.com/bid/40291
http://www.openwall.com/lists/oss-security/2010/06/21/1
http://www.openwall.com/lists/oss-security/2010/05/25/9
http://www.openwall.com/lists/oss-security/2010/05/25/3
http://www.mandriva.com/security/advisories?name=MDVSA-2010:120
http://squirrelmail.org/security/issue/2010-06-21
http://secunia.com/advisories/40307
http://lists.fedoraproject.org/pipermail/package-announce/2010-June/043261.html
http://lists.fedoraproject.org/pipermail/package-announce/2010-June/043258.html
http://lists.fedoraproject.org/pipermail/package-announce/2010-June/043239.html
http://lists.apple.com/archives/security-announce/2012/Feb/msg00000.html