Microsoft Security Bulletin (MS99-042)

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Microsoft Security Bulletin (MS99-042)
--------------------------------------

Patch Available for "IFRAME ExecCommand" Vulnerability
Originally Posted: October 11, 1999
Updated: October 15, 1999

Summary
=======
On October 11, 1999, Microsoft released the original version of this
bulletin, in order to advise customers of a workaround for a vulnerability
in Microsoft(r) Internet Explorer. The vulnerability could allow a malicious
web site operator to read files on the computer of a user who visited the
site, under certain circumstances. Microsoft has completed a patch that
completely eliminates the vulnerability, and has re-released this bulletin
in order to advise customers of its availability.

Frequently asked questions regarding this vulnerability can be found
at http://www.microsoft.com/security/bulletins/MS99-042faq.asp.

Issue
=====
The Internet Explorer security model normally restricts the
Document.ExecCommand() method to prevent it from taking inappropriate action
on a user's computer. However, at least one of these restrictions is not
present if the method is invoked on an IFRAME. This could allow a malicious
web site operator to read the contents of files on visiting users'
computers, if he or she knew the name of the file and the folder in which it
resided. The vulnerability would not allow the malicious user to list the
contents of folders, create, modify or delete files, or to usurp any
administrative control over the machine.

A patch that corrects this vulnerability is available at the location
discussed below. This patch also includes the previously-released fix for
the "Download Behavior" vulnerability.

Affected Software Versions
==========================
 - Microsoft Internet Explorer 4.01, versions prior
   to Service Pack 2
 - Microsoft Internet Explorer 5

Patch Availability
==================
Internet Explorer 4.01 users should apply IE 4.01 Service Pack 2 at:
 - http://www.microsoft.com/windows/ie/download/windows.htm

Internet Explorer 5 should apply that patch for this vulnerability at:
 - Intel Platform: ftp://ftp.microsoft.com/peropsys/IE/IE-Public/Fixes/
   usa/IE50/MSHTML-fix/x86/q243638.exe
 - Alpha Platform: ftp://ftp.microsoft.com/peropsys/IE/IE-Public/Fixes/
   usa/IE50/MSHTML-fix/Alpha/q243638.exe

NOTE: Line breaks have been inserted into the URLs above to improve
readability.

NOTE: The IE5 patch also includes the previously-released fix for the
"Download Behavior" vulnerability, discussed in
http://www.microsoft.com/security/bulletins/ms99-040.asp.

NOTE: The IE5 patch also will be available shortly at
http://windowsupdate.microsoft.com. When this happens, this bulletin
will be modified to provide the download location.

More Information
================
Please see the following references for more information related to this
issue.

 - Microsoft Security Bulletin MS99-042: Frequently Asked Questions,
   http://www.microsoft.com/security/bulletins/MS99-042faq.asp.
 - Microsoft Knowledge Base (KB) article Q243638,
   Update Available for "IFRAME ExecCommand" Vulnerability in Internet
   Explorer 5,
   http://support.microsoft.com/support/kb/articles/q243/6/38.asp.
   (Note: It may take 24 hours from the original posting of this bulletin
   for this KB article to be visible.)
 - Microsoft Security Advisor web site,
   http://www.microsoft.com/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 acknowledges Georgi Guninski for bringing this issue to our
attention.

Revisions
=========
 - October 11, 1999: Bulletin Created.
 - October 15, 1999: Bulletin re-released to provide information on
   availability of patch.

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