When an incoming Web request is made to a computer that is running Internet Security and Acceleration (ISA) Server and is publishing a Web page by using Web Publishing, the Web Proxy service may stop and an access violation may occur.

This problem can occur if you use Web Publishing to bridge incoming Hypertext Transfer Protocol (HTTP) traffic to a Web server behind ISA Server; a malformed URL request might cause the Web Proxy service to stop and an access violation might occur. This problem occurs because of a heap corruption, not a buffer overrun, and does not compromise access to ISA Server from the Internet in any way. The Web Proxy service, Web proxy clients, and sites that are made available by Web Publishing are affected by this problem. If you do not have listeners configured under Incoming Web Requests (these listeners are not configured by default), this problem does not affect ISA Server in any way.

A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that you determine are at risk of attack. Evaluate your computer's physical accessibility, network and Internet connectivity, and other factors to determine the degree of risk to your computer. See the associated Microsoft Security Bulletin (http://www.microsoft.com/technet/security/bulletin/MS01-021.mspx) to help determine the degree of risk. This fix may receive additional testing. If your computer is sufficiently at risk, Microsoft recommends that you apply this fix now. Otherwise, wait for the next ISA Server service pack that contains this fix.

To resolve this problem immediately, download the fix by following the instructions later in this article or contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:NOTE: In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The following file is available for download from the Microsoft Download Center:
For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file. The English, French, German, Spanish, and Japanese versions of this fix should have the following file attributes or later:
To install the fix, run the self-extracting file. You do not need to restart the computer. Start and stop the Web Proxy service by opening the ISA Server Management Console and then clicking Monitoring. Stop and start the Web Proxy service. If this computer is in an array, you do not need to shut the whole array down; you can still install this fix on a one-by-one basis.

This fix applies to the French, German, Spanish, and Japanese versions of ISA Server as well.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

For more information on this vulnerability, see the following Microsoft Web site: