Microsoft Security Bulletin (MS00-042)

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Patch Available for "Active Setup Download" Vulnerability
Originally Posted: June 29, 2000

Summary
=======
Microsoft has released a patch that eliminates a security
vulnerability in an ActiveX  control that ships with Microsoft(r)
Internet Explorer. The vulnerability could be used to  overwrite
files on the computer of a user who visited a malicious web site
operator's  site.

Frequently asked questions regarding this vulnerability
and the patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-042.asp

Issue
=====
The Active Setup Control allows .cab files to be downloaded to a
user's computer as part  of the installation process for software
updates. However, the control has two flaws.  First, it treats all
Microsoft-signed .cab files as trusted, thereby allowing them to be
installed without asking the user's approval. Second, it provides a
method by which the  caller can specify a download location on the
user's hard drive. In combination, these two  flaws would allow a
malicious web site operator to download a Microsoft-signed .cab file
as a means of overwriting a file on the user's machine. By
overwriting system files, this  could allow the malicious user to
render the machine unusable.

It is important to note that there is no capability via this
vulnerability to actually  install the software that has been
downloaded - the vulnerability only allows files to be  overwritten,
in a denial of service attack. System File Protection in Windows 2000
would  prevent an attack like this one from being used to overwrite
system files.

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/patch8.htm

Note: The patch also will be available shortly on WindowsUpdate. When
this happens, we  will modify this bulletin to provide specific
information on obtaining it.

Note: The patches require IE 4.01 Service Pack 2 or IE 5.01 to
install. Customers using  versions prior to 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 Q265258.

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 MS00-042,
   http://www.microsoft.com/technet/security/bulletin/fq00-042.asp
 - Microsoft Knowledge Base article Q265258 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 Juan Carlos Garcia Cuartango of Spain for reporting
this issue to us and  working with us to protect customers.

Revisions
June 29, 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 29,2000

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

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