Microsoft Security Bulletin (MS99-050)

[aleph1 () UNDERGROUND ORG (Aleph One)]

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Microsoft Security Bulletin (MS99-050)
--------------------------------------

Patch Available for "Server-side Page Reference Redirect" Vulnerability
Originally Posted: December 08, 1999

Summary
=======
Microsoft has released a patch that eliminates a vulnerability in
Microsoft(r) Internet Explorer  4.01, 5 and 5.01, that could allow a
malicious web site operator to view a file on the computer  of a visiting
user, provided that the web site operator knew the name and folder of the
file.

Frequently asked questions regarding this vulnerability can be found at
http://www.microsoft.com/security/bulletins/MS99-050faq.asp.

Issue
=====
When a web server performs a server-side redirect, the IE security model
checks the server's  permissions on the new page. However, under favorable
timing conditions, it is possible for a web  server to create a reference to
a client window that the server is permitted to view, then use a
server-side redirect to a client-local file, and bypass the security
restrictions. The result is  that it could be possible for a malicious web
site operator to view files on the computer of a  visiting user. The web
site operator would need to know (or guess) the name and location of the
file.

Affected Software Versions
==========================
 - Microsoft Internet Explorer 4.01
 - Microsoft Internet Explorer 5.0
 - Microsoft Internet Explorer 5.01

Patch Availability
==================
 - http://www.microsoft.com/windows/ie/security/servredir.asp

NOTE: This patch also includes the previously-released patch for the
"ImportExportFavorites"  vulnerability.

NOTE: This and other patches are available from the Microsoft
Download Center (http://www.microsoft.com/downloads/search.asp?
Search=Keyword&Value='security_patch'&OpSysID=1)

NOTE: Microsoft produces security patches for Internet Explorer 4.01 SP2 and
higher. In the event  that this package is applied to Internet Explorer 4.01
SP1, the package states that a fix is not  needed. This message is
incorrect, as the vulnerability does exist on Internet Explorer 4.01 SP1  or
any earlier release. If you are using Internet Explorer 4.01 SP1 or any
earlier release,  please upgrade to the latest version of Internet Explorer
to resolve this issue.

NOTE: The patch will be available shortly at the WindowsUpdate site. When
this happens, we will  modify the bulletin to provide additional
information.

More Information
================
Please see the following references for more information related to this
issue.
 - Microsoft Security Bulletin MS99-050: Frequently Asked Questions,
   http://www.microsoft.com/security/bulletins/MS99-050faq.asp.
 - Microsoft Knowledge Base (KB) article Q246094,
   Update Available for "Server-side Page Reference Redirect"
   Vulnerability,
   http://support.microsoft.com/support/kb/articles/q246/0/94.asp.
   (NOTE: It may take 24 hours from the original posting of this bulletin
   for this KB article to be visible.)
 - 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.

Revisions
=========
 - December 08, 1999: Bulletin Created

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