The ISA Firewall service in Microsoft Internet Security and Acceleration (ISA) Server 2000 allows remote attackers to cause a denial of service (Wspsrv.exe crash) via a large amount of SecureNAT network traffic.
http://www.securityfocus.com/bid/13846
http://www.niscc.gov.uk/niscc/docs/br-20050602-00456.html?lang=en
http://www.networksecurity.fi/advisories/windows-isa-firewall.html
http://support.microsoft.com/default.aspx?scid=kb%3B%5BLN%5D%3B894864