Microsoft Patches Spoofing Flaw in ISA Server

Through a flaw in Microsoft's Internet Security and Acceleration Server 2000 and Proxy Server 2.0, users could be served content from malicious sites in lieu of the trusted content they requested.

Microsoft has issued a patch for a flaw in ISA (Internet Security and Acceleration) Server 2000 and Proxy Server 2.0. According to the advisory on the bug, it could allow an attacker to spoof trusted Internet content.

Microsoft Small Business Server 2000 and 2003, both of which include ISA Server, are also affected.

If a user could first be persuaded to visit a particular site, the attack could allow that site to serve that content instead of content from other sites the user believes he is visiting.

The bug would not allow the spoofing of an SSL (Secure Sockets Layer) certificate, and if a spoofed site attempts to use a trusted Web sites SSL certificate, the authentication will fail.

Because of these mitigating circumstances, Microsoft has termed the problem "important" as opposed to the more severe "critical rating."

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Patches are available through links on the advisory page. It is also possible to work around the bug by setting the DNS (Domain Name System) cache size to 0, thus preventing the spoofed site from serving data from the cache, but this would have a deleterious effect on performance and defeat much of the point of running ISA Server.

This patch was the first for which Microsoft gave advance notice, in accordance with a new policy. Three business days prior to the release of such advisories, Microsoft will release information on the number of such advisories, the products they affect and their severity.

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