asterisk<1.8.7.2: Remote crash possibility with SIP and the “automon” feature enabled (2.3)
When the “automon” feature is enabled in features.conf, it is possible to send a sequence of SIP requests that cause Asterisk to dereference a NULL pointer and crash.
http://downloads.asterisk.org/pub/security/AST-2011-014.html
(from redmine: issue id 858, created on 2011-12-09, closed on 2011-12-22)