The IAX2 channel driver (chan_iax2) in Asterisk Open 1.2.x before 1.2.23, 1.4.x before 1.4.9, and Asterisk Appliance Developer Kit before 0.6.0, when configured to allow unauthenticated calls, allows remote attackers to cause a denial of service (resource exhaustion) via a flood of calls that do not complete a 3-way handshake, which causes an ast_channel to be allocated but not released.
bugs.gentoo.org/show_bug.cgi?id=185713
ftp.digium.com/pub/asa/ASA-2007-018.pdf
osvdb.org/38197
secunia.com/advisories/26274
secunia.com/advisories/29051
security.gentoo.org/glsa/glsa-200802-11.xml
securityreason.com/securityalert/2960
www.securityfocus.com/archive/1/475069/100/0/threaded
www.securityfocus.com/bid/24950
www.securitytracker.com/id?1018472
www.vupen.com/english/advisories/2007/2701