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.