Microsoft Security Bulletin (MS00-076)

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Microsoft Security Bulletin (MS00-076)
- --------------------------------------

Patch Available for "Cached Web Credentials" Vulnerability

Originally posted: October 12, 2000

Summary
=======
Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) Internet Explorer. Under a daunting
set of conditions, the vulnerability could enable a malicious user to
obtain another user's userid and password to a web  site.

Frequently asked questions regarding this vulnerability
and the patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-076.asp

Issue
=====
When a user authenticates to a secured web page via Basic
Authentication, IE caches the userid and password that were used,  in
order to minimize the number of times the user must authenticate to
the same site. By design, IE should only send the  cached credentials
to secured pages on the site. However, it will actually send them to
non-secure pages on the site as well.  If a malicious user had
complete control of another user's network communications, he could
wait until another user logged  onto a secured site, then spoof a
request for a non-secured page in order to collect the credentials.

The vulnerability does not provide a means by which the malicious
user could force the other user to log onto a secure page  of his
choice, and could only be used to reveal credentials that had been
cached during the current IE session.

Affected Software Versions
==========================
 - Microsoft Internet Explorer 4.x
 - Microsoft Internet Explorer 5.x prior to version 5.5

Note: Internet Explorer 5.5 is not affected by this vulnerability.
Customers using IE 5.5 do not need to take any action.

Patch Availability
==================
 - http://www.microsoft.com/windows/ie/download/critical/q273868.htm

Note: The patch requires IE 5.01 SP1 to install. Customers who
install this patch on other versions may receive a message  reading
"This update does not need to be installed on this system". This
message is incorrect. More information is available  in KB article
Q273868.

Note: As discussed in Affected Software Versions, this vulnerability
does not affect IE 5.5.

Note: Per the normal security support policy for IE, security patches
for Internet Explorer version 4.x are no longer being  produced.
Microsoft recommends that IE 4.x customers who are concerned about
this issue consider upgrading to either IE 5.01  SP1 or IE 5.5.

Note: The fix for this issue will be included in IE 5.01 SP2.

Note: Additional security patches are available at the Microsoft
Download Center

More Information
================
Please see the following references for more information related to
this issue.
 - Frequently Asked Questions: Microsoft Security Bulletin MS00-076,
   http://www.microsoft.com/technet/security/bulletin/fq00-076.asp
 - Microsoft Knowledge Base article Q273868 discusses this issue
   and will be available soon.
 - Microsoft TechNet Security web site,
   http://www.microsoft.com/technet/security/default.asp

Obtaining Support on this Issue
===============================
This is a fully supported patch. Information on contacting Microsoft
Product
Support Services is available at
http://support.microsoft.com/support/contact/default.asp.

Acknowledgments
===============
Microsoft thanks ACROS Security (http://www.acros.si) for reporting
this issue to us and working with us to protect  customers.

Revisions
=========
 - October 12, 2000: Bulletin Created.

- ------------------------------------------------

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED
"AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT  DISCLAIMS ALL
WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR  PURPOSE. IN NO EVENT
SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY
DAMAGES WHATSOEVER INCLUDING DIRECT,  INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS  SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF  LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Last Updated October 12, 2000

(c) 2000 Microsoft Corporation. All rights reserved. Terms of use.


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