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Microsoft Security Bulletin (MS99-054)
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Patch Available for "WPAD Spoofing" Vulnerability
Originally Posted: December 01, 1999
Summary
=======
Microsoft has released a version upgrade that eliminates a vulnerability in
Microsoft(r) 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/security/bulletins/MS99-054faq.asp.
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 hostname 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
Patch Availability
==================
The vulnerability is eliminated by IE 5.01, which is available at:
- http://www.microsoft.com/windows/ie/download/all.htm?bShowPage
- http://www.microsoft.com/msdownload/iebuild/
ie501_win32/en/ie501_win32.htm
A line break has been inserted into the above URL for readability.
More Information
================
Please see the following references for more information related to this
issue.
- Frequently Asked Questions: Microsoft Security Bulletin MS99-054,
http://www.microsoft.com/security/bulletins/ms99-054faq.asp.
- Microsoft Knowledge Base (KB) article Q247333,
Web Proxy Auto-Discovery "Spoofing" May Change Proxy Settings,
http://support.microsoft.com/support/kb/articles/q247/7/33.asp.
(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://ietf.org/internet-drafts/draft-ietf-wrec-wpad-01.txt.
- Microsoft Security Advisor web site,
http://www.microsoft.com/security/default.asp.
Obtaining Support on this Issue
===============================
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
http://support.microsoft.com/support/contact/default.asp.
Acknowledgments
===============
Microsoft acknowledges Tim Adam of Open Software Associates (www.osa.com)
for bringing this issue to our attention.
Revisions
=========
- December 01, 1999: Bulletin Created.
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