Niels Provos libevent 1.2 and 1.2a allows remote attackers to cause a denial of service (infinite loop) via a DNS response containing a label pointer that references its own offset.
http://www.vupen.com/english/advisories/2007/0647
http://www.securityfocus.com/bid/22606
http://www.securityfocus.com/archive/1/460530/100/0/threaded
http://securityreason.com/securityalert/2268