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Microsoft Security Bulletin MS99-054 - Critical

Patch Available for "WPAD Spoofing" Vulnerability

Published: December 01, 1999

Version: 1.0

Originally Posted: December 01, 1999

Summary

Microsoft has released a version upgrade that eliminates a vulnerability in Microsoft® Internet Explorer 5. Under very specific conditions, the vulnerability could allow a malicious user to provide proxy settings to web clients in another network.

Frequently asked questions regarding this vulnerability can be found at http://www.microsoft.com/technet/security/bulletins/fq99-054.mspx.

Issue

The IE 5 Web Proxy Auto-Discovery (WPAD) feature enables web clients to automatically detect proxy settings without user intervention. The algorithm used by WPAD prepends the hostname "wpad" to the fully-qualified domain name and progressively removes subdomains until it either finds a WPAD server answering the domain name or reaches the third-level domain. For instance, web clients in the domain a.b.microsoft.com would query wpad.a.b.microsoft, wpad.b.microsoft.com, then wpad.microsoft.com. A vulnerability arises because in international usage, the third-level domain may not be trusted. A malicious user could set up a WPAD server and serve proxy configuration commands of his or her choice.

Affected Software Versions

  • Microsoft Internet Explorer 5

Vulnerability Identifier: CVE-1999-0858

Patch Availability

The vulnerability is eliminated by IE 5.01, which is available at:

More Information

Please see the following references for more information related to this issue.

Obtaining Support on this Issue

This is a fully supported patch. Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/contactussupport/?ws=support.

Acknowledgments

Microsoft acknowledges Tim Adam of Open Software Associates for bringing this issue to our attention.

Revisions

  • December 01, 1999: Bulletin Created.

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