Microsoft Security Bulletin MS99-054 - Critical
Patch Available for "WPAD Spoofing" Vulnerability
Published: December 01, 1999
Originally Posted: December 01, 1999
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.
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
The vulnerability is eliminated by IE 5.01, which is available at:
Please see the following references for more information related to this issue.
- Frequently Asked Questions: Microsoft Security Bulletin MS99-054, http://www.microsoft.com/technet/security/bulletins/fq99-054.mspx.
Microsoft Knowledge Base (KB) article 247333, Web Proxy Auto-Discovery "Spoofing" May Change Proxy Settings, http://support.microsoft.com/default.aspx?scid=kb;en-us;247333&sd=tech.
(Note: It may take 24 hours from the original posting of this bulletin for this KB article to be visible.)
Web Proxy Auto-Discovery Protocol Internet Draft, http://www3.ietf.org/proceedings/99nov/I-D/draft-ietf-svrloc-wpad-template-00.txt.
- Microsoft Security Advisor web site, http://www.microsoft.com/security/default.mspx.
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.
Microsoft acknowledges Tim Adam of Open Software Associates for bringing this issue to our attention.
- December 01, 1999: Bulletin Created.
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