The decode_choice function in net/netfilter/nf_conntrack_h323_asn1.c in the Linux kernel before 2.6.20.15, 2.6.21.x before 2.6.21.6, and before 2.6.22 allows remote attackers to cause a denial of service (crash) via an encoded, out-of-range index value for a choice field, which triggers a NULL pointer dereference.
http://www.vupen.com/english/advisories/2007/2466
http://www.ubuntu.com/usn/usn-510-1
http://www.securityfocus.com/bid/24818
http://www.mandriva.com/security/advisories?name=MDKSA-2007:195
http://www.debian.org/security/2007/dsa-1356
http://secunia.com/advisories/27212
http://secunia.com/advisories/26450
http://secunia.com/advisories/25955
http://kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.22
http://kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.21.6