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Microsoft Security Bulletin (MS99-054)
From: aleph1 () UNDERGROUND ORG (Aleph One)
Date: Thu, 2 Dec 1999 10:48:12 -0800


The following is a Security  Bulletin from the Microsoft Product Security
Notification Service.

Please do not  reply to this message,  as it was sent  from an unattended
mailbox.
                    ********************************

Microsoft Security Bulletin (MS99-054)
--------------------------------------

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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