A security vulnerability exists in the H.323 filter for Microsoft Internet Security and Acceleration Server 2000 that could allow an attacker to overflow a buffer in the Microsoft Firewall Service in Microsoft Internet Security and Acceleration Server 2000. An attacker who successfully exploited this vulnerability could try to run code of their choice in the security context of the Microsoft Firewall Service. This would give the attacker complete control over the system. The H.323 filter is enabled by default on servers running ISA Server 2000 computers that are installed in integrated or firewall mode.
ISA Servers running in cache mode are not vulnerable because the Microsoft Firewall Service is disabled by default
Users can prevent the risk of attack by disabling the H.323 filter