The Manager Interface in Asterisk before 1.2.18 and 1.4.x before 1.4.3 allows remote attackers to cause a denial of service (crash) by using MD5 authentication to authenticate a user that does not have a password defined in manager.conf, resulting in a NULL pointer dereference.
https://exchange.xforce.ibmcloud.com/vulnerabilities/33886
http://www.vupen.com/english/advisories/2007/1534
http://www.securitytracker.com/id?1017955
http://www.securityfocus.com/bid/23649
http://www.securityfocus.com/archive/1/466911/100/0/threaded
http://www.novell.com/linux/security/advisories/2007_34_asterisk.html
http://www.debian.org/security/2007/dsa-1358
http://www.asterisk.org/files/ASA-2007-012.pdf
http://securityreason.com/securityalert/2646