INFORMATION BULLETIN INFORMATION BULLETIN 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.
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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.
DOE-CIRC can be contacted at:
Voice: +1 866-941-2472 (7 x 24)
E-mail: doecirc@doecirc.energy.gov
World Wide Web: http://www.doecirc.energy.gov/