vlan_dev.c in the VLAN code for Linux kernel 2.6.8 allows remote attackers to cause a denial of service (kernel oops from null dereference) via certain UDP packets that lead to a function call with the wrong argument, as demonstrated using snmpwalk on snmpd.
http://www.securityfocus.com/bid/14611
http://www.mandriva.com/security/advisories?name=MDKSA-2005:219
http://www.debian.org/security/2005/dsa-922
http://secunia.com/advisories/18056
http://secunia.com/advisories/17826
http://lists.osdl.org/pipermail/bridge/2004-September/000638.html