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Microsoft Security Bulletin (MS00-039)
- --------------------------------------

Patch Available for "SSL Certificate Validation" Vulnerabilities

Originally posted: June 05, 2000

Summary
=======
Microsoft has released a patch that eliminates two security
vulnerabilities in Microsoft(r) Internet Explorer. The
vulnerabilities involve how IE handles digital certificates; under a
very daunting set of circumstances, they could allow a  malicious web
site operator to pose as a trusted web site.

In addition to eliminating the "SSL Certificate Validation"
vulnerabilities, this patch also eliminates all vulnerabilities
discussed in Microsoft Security Bulletin MS00-033.

Frequently asked questions regarding this vulnerability and the
patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-039.asp

Issue
=====
Two vulnerabilities have been identified in the way IE handles digital
certificates:
 - When a connection to a secure server is made via either an
   image or a frame, IE only verifies that the server's SSL
   certificate was issued by a trusted root - it does not verify the
   server name or the expiration date. When a connection is made via
   any other means, all expected validation is performed.
 - Even if the initial validation is made correctly, IE does not
   re-validate the certificate if a new SSL session is established
   with the same server during the same IE session.

The circumstances under which these vulnerabilities could be exploited
are fairly restricted. In both cases, it is likely  that the attacker
would need to either carry out DNS cache poisoning or physically
replace the server in order to  successfully carry out an attack via
this vulnerability. The timing would be especially crucial in the
second case, as the  malicious user would need to poison the cache or
replace the machine during the interregnum between the two SSL
sessions.

Affected Software Versions
==========================
 - Microsoft Internet Explorer 4.0
 - Microsoft Internet Explorer 4.01
 - Microsoft Internet Explorer 5.0
 - Microsoft Internet Explorer 5.01

Patch Availability
==================
 - http://www.microsoft.com/windows/ie/download/critical/patch7.htm

Note: This patch also eliminates all vulnerabilities discussed in
Microsoft Security Bulletin MS00-033.

Note: The patch requires IE 5.01 to install; a version that supports
IE 4.01 Service Pack 2 will be released shortly.  Customers who
install this patch on versions other than these 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
Q254902.

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 MS00-039,
   http://www.microsoft.com/technet/security/bulletin/fq00-039.asp
 - Microsoft Knowledge Base article Q254902 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
Technical
Support is available at
http://support.microsoft.com/support/contact/default.asp.

Acknowledgments
===============
Microsoft thanks the ACROS Penetration Team, Slovenia, for reporting
this issue to us and working with us to protect  customers.

Revisions
=========
 - June 05, 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 June 05,2000

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


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