Squid 2.5 STABLE9 and earlier, when the DNS client port is unfiltered and the environment does not prevent IP spoofing, allows remote attackers to spoof DNS lookups.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A9976
http://www.vupen.com/english/advisories/2005/0521
http://www.squid-cache.org/Versions/v2/2.5/bugs/#squid-2.5.STABLE9-dns_query
http://www.securityfocus.com/bid/13592
http://www.redhat.com/support/errata/RHSA-2005-489.html
http://www.redhat.com/archives/fedora-announce-list/2005-May/msg00025.html
http://www.debian.org/security/2005/dsa-751