The PJSIP Channel Driver in Asterisk Open Source before 12.3.1 allows remote attackers to cause a denial of service (deadlock) by terminating a subscription request before it is complete, which triggers a SIP transaction timeout.
http://www.securityfocus.com/archive/1/532416/100/0/threaded
http://packetstormsecurity.com/files/127090/Asterisk-Project-Security-Advisory-AST-2014-008.html
http://downloads.asterisk.org/pub/security/AST-2014-008.html