The following is a Security Bulletin from the Microsoft Product Security
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Patch Available for "Active Setup Download" Vulnerability
Originally Posted: June 29, 2000
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
Frequently asked questions regarding this vulnerability
and the patch can be found at
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
Affected Software Versions
- Microsoft Internet Explorer 4.0
- Microsoft Internet Explorer 4.01
- Microsoft Internet Explorer 5.0
- Microsoft Internet Explorer 5.01
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
Please see the following references for more information related to
- Frequently Asked Questions: Microsoft Security Bulletin MS00-042,
- Microsoft Knowledge Base article Q265258 discusses this issue and
will be available soon.
- Microsoft TechNet Security web site,
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
Microsoft thanks Juan Carlos Garcia Cuartango of Spain for reporting
this issue to us and working with us to protect customers.
June 29, 2000: Bulletin Created.
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SO THE FOREGOING LIMITATION MAY NOT APPLY.
Last Updated June 29,2000
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