Asterisk Open Source 12.x before 12.8.1 and 13.x before 13.1.1, when using the PJSIP channel driver, does not properly reclaim RTP ports, which allows remote authenticated users to cause a denial of service (file descriptor consumption) via an SDP offer containing only incompatible codecs.
http://www.securitytracker.com/id/1031661
http://www.securityfocus.com/archive/1/534573/100/0/threaded
http://seclists.org/fulldisclosure/2015/Jan/116
http://downloads.asterisk.org/pub/security/AST-2015-001.html