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ISA, Proxy Server Vulnerable to DoS Attack

Microsoft Internet Security & Acceleration Server and Proxy Server 2.0 are vulnerable to a denial-of-service attack due to a flaw in the way services in the two products handle a response from remote clients.

Microsoft rated the issue as "Important" on its vulnerability threat scale and encouraged administrators to patch systems "at the earliest available opportunity." A bulletin describing the vulnerability and providing a patch can be found at www.microsoft.com/technet/security/bulletin/MS03-012.asp.

The vulnerability is open to attackers on an internal networks who would send a specially crafted packet that would cause the server to stop responding to internal and external requests. CPU utilization reaches 100 percent, making the server unresponsive. Microsoft acknowledged that an Internet-based attack is possible but rare because the default settings prevent it.

ISA Server is affected when being used as a firewall because the vulnerability occurs in the Microsoft Firewall Service on that product. When used strictly as a caching server, ISA 2000 is not vulnerable.

In Proxy Server 2.0, it is the Winsock Proxy service that presents the flaw. Previous versions of Proxy Server are not supported and weren't tested.

About the Author

Scott Bekker is editor in chief of Redmond Channel Partner magazine.

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