The IPv6 support in Windows XP SP2, 2003 Server SP1, and Longhorn, with Windows Firewall turned off, allows remote attackers to cause a denial of service (CPU consumption) via a TCP packet with the SYN flag set and the same destination and source address and port, a variant of CVE-2005-0688 and a reoccurrence of the "Land" vulnerability (CVE-1999-0016).