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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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