chan_iax2.c in the IAX2 channel driver in Certified Asterisk 1.8.11-cert before 1.8.11-cert2 and Asterisk Open Source 1.8.x before 1.8.12.1 and 10.x before 10.4.1, when a certain mohinterpret setting is enabled, allows remote attackers to cause a denial of service (daemon crash) by placing a call on hold.
http://www.securitytracker.com/id?1027102
http://www.debian.org/security/2012/dsa-2493
http://secunia.com/advisories/49303
http://downloads.asterisk.org/pub/security/AST-2012-007.html