res/res_pjsip_exten_state.c in the PJSIP channel driver in Asterisk Open Source 12.x before 12.1.0 allows remote authenticated users to cause a denial of service (crash) via a SUBSCRIBE request without any Accept headers, which triggers an invalid pointer dereference.
https://issues.asterisk.org/jira/browse/ASTERISK-23139
http://lists.fedoraproject.org/pipermail/package-announce/2014-March/130426.html
http://lists.fedoraproject.org/pipermail/package-announce/2014-March/130400.html
http://downloads.asterisk.org/pub/security/AST-2014-004.html
http://downloads.asterisk.org/pub/security/AST-2014-004-12.diff