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Microsoft "Active Setup Download" Vulnerability
Microsoft "Active Setup Download" Vulnerability Privacy and Legal Notice

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K-057: Microsoft "Active Setup Download" Vulnerability

June 30, 2000 15:00 GMT


PROBLEM:       The Microsoft Active Setup Control has an internal flaw which
               allows the downloading of a trusted ".cab" file to any disk
               location.
PLATFORM:      All Microsoft systems, except for Windows 2000, running the
               following software:
                    Microsoft Internet Explorer 4.0
                    Microsoft Internet Explorer 4.01
                    Microsoft Internet Explorer 5.0
                    Microsoft Internet Explorer 5.01
DAMAGE:        A malicious web site could download a ".cab" file to any
               location on a users system, overwriting any system file. The
               overwriting of system files could render a machine inoperable,
               making a denial of service (DoS).
SOLUTION:      Install the Microsoft patch.


VULNERABILITY The risk is MEDIUM. The capability to exploit this vulnerability ASSESSMENT: currently exists. The exploit has been publicly announced.



Cabinet File Description

Cabinet files have extensions of ".cab".  These files have been used by
Microsoft and others, as a software distribution medium.  Typically a cabinet
file contains compressed files, which are automatically decompressed on
installation.  Within a cabinet file multiple files may be combinded
into what is termed a 'folder'.  Cabinet files are used to reduce file download
size and related download times.  Microsoft uses cabinet files in a wide
variety of software.  Cabinet files may be found in Microsoft service
packs, Miscrosoft Powerpoint, Microsoft Office (Windows version), and
other products.  Large files may span more than one cabinet file.  Java
and ActiveX commands may be embeded into cabinet files.  The running
of Java and ActiveX commands are determined by the security permissions
used when signing the cabinet file.  Cabinet files may be digitally signed
in a manner similar to ActiveX Control files.

It can be expected that users will continue to encounter cabinet files
in the future.

[******  Begin Microsoft Bulletin  ******]


Microsoft Security Bulletin (MS00-042)
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.

[******  End Microsoft Bulletin  ******]




CIAC wishes to acknowledge the contributions of Microsoft for the information contained in this bulletin.

CIAC services are available to DOE, DOE Contractors, and the NIH. CIAC can be contacted at:
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    World Wide Web:  http://www.ciac.org/
                     http://ciac.llnl.gov
                     (same machine -- either one will work)
    Anonymous FTP:   ftp.ciac.org
                     ciac.llnl.gov
                     (same machine -- either one will work)

This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.
UCRL-MI-119788
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