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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