The IAX2 channel driver (chan_iax2) in Asterisk before 1.2.22 and 1.4.x before 1.4.8 Business Edition before B.2.2.1 AsteriskNOW before beta7 Appliance Developer Kit before 0.5.0 and s800i before 1.0.2 allows remote attackers to cause a denial of service (crash) via a crafted (1) LAGRQ or (2) LAGRP frame that contains information elements of IAX frames which results in a NULL pointer dereference when Asterisk does not properly set an associated variable.