Microsoft Patches Spoofing Flaw in ISA Server

By Larry Seltzer  |  Posted 2004-11-09 Print this article Print

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."

Click here for reviews of SSL-based VPNs. 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.

Check out eWEEK.coms for the latest security news, reviews and analysis. And for insights on security coverage around the Web, take a look at Security Center Editor Larry Seltzers Weblog.
Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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