The aclMatchExternal function in Squid before 2.6.STABLE7 allows remote attackers to cause a denial of service (crash) by causing an external_acl queue overload, which triggers an infinite loop.
https://exchange.xforce.ibmcloud.com/vulnerabilities/31525
http://www.vupen.com/english/advisories/2007/0199
http://www.ubuntu.com/usn/usn-414-1
http://www.squid-cache.org/bugs/show_bug.cgi?id=1848
http://www.squid-cache.org/Versions/v2/2.6/squid-2.6.STABLE7-RELEASENOTES.html#s12
http://www.securityfocus.com/bid/22203
http://www.novell.com/linux/security/advisories/2007_12_squid.html
http://www.mandriva.com/security/advisories?name=MDKSA-2007:026
http://www.gentoo.org/security/en/glsa/glsa-200701-22.xml
http://secunia.com/advisories/23946
http://secunia.com/advisories/23921
http://secunia.com/advisories/23889