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Microsoft Security Bulletin (MS99-040)

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Patch Available for "Download Behavior" Vulnerability

Originally Posted: September 28, 1999

Updated: October 08, 1999



Summary

=======

On September 28, 1999, Microsoft released the original version of this

bulletin, in order to  provide a workaround for a security vulnerability in

Microsoft(r) Internet Explorer 5 that could  allow a malicious web site

operator to read files on the computer of a person who visited the  site.

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/MS99-040faq.asp.



Issue

=====

IE 5 includes a feature called "download behavior" that allows web page

authors to download files  for use in client-side script. By design, a web

site should only be able to download files that  reside in its domain; this

prevents client-side code from exposing files on the user's machine or

local intranet to the web site. However, a server-side redirect can be used

to bypass this  restriction, thereby enabling a malicious web site operator

to read files on the user's machine  or the user's local intranet. This

vulnerability would chiefly affect workstations that are  connected to the

Internet.



Affected Software Versions

==========================

 - Microsoft Internet Explorer 5



Patch Availability

==================

The patch is available for download at either of the following locations

 - http://windowsupdate.microsoft.com

 - http://www.microsoft.com/msdownload/iebuild/dlbhav/en/dlbhav.htm



More Information

================

Please see the following references for more information related to this

issue.

 - Microsoft Security Bulletin MS99-040: Frequently Asked Questions,

   http://www.microsoft.com/security/bulletins/ms99-040faq.asp.

 - Microsoft Knowledge Base (KB) article Q242542,

   "Download Behavior" Vulnerability in Internet Explorer 5,

   http://support.microsoft.com/support/kb/articles/Q242/5/42.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

===============================

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

=========

 - September 28, 1999: Bulletin Created.

 - October 08, 1999: Bulletin updated to announce availability of patch.



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