ConfBridge in Asterisk 11.x before 11.14.1 and Certified Asterisk 11.6 before 11.6-cert8 does not properly handle state changes, which allows remote attackers to cause a denial of service (channel hang and memory consumption) by causing transitions to be delayed, which triggers a state change from hung up to waiting for media.
http://seclists.org/fulldisclosure/2014/Nov/67
http://downloads.asterisk.org/pub/security/AST-2014-014.html