__________________________________________________________
The U.S. Department of Energy
Computer Incident Advisory Capability
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/ | /_\ /
\___ __|__ / \ \___
__________________________________________________________
INFORMATION BULLETIN
Microsoft IE 5 Vulnerability - "download behavior"
October 13, 1999 17:00 GMT Number K-002
______________________________________________________________________________
PROBLEM: A security vulnerability in Microsoft Internet Explorer 5
may allow a malicious web site operator to read files on the
computer of a person who visited the site.
PLATFORM: Microsoft Windows 95/98 and NT running Internet Explorer 5
DAMAGE: A malicious web site operator may read files on a computer
visiting their site. The vulnerability would not allow files to
be created, deleted or modified.
SOLUTION: Load the Hotfix.
______________________________________________________________________________
VULNERABILITY The risk is low. A user would have to visit a web site and view
ASSESSMENT: a web page constructed to exploit this vulnerability.
______________________________________________________________________________
[ Start Microsoft Advisory ]
Microsoft Security Bulletin (MS99-040)
--------------------------------------
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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[ End Microsoft Advisory ]
______________________________________________________________________________
CIAC wishes to acknowledge the contributions of Microsoft for the
information contained in this bulletin.
______________________________________________________________________________
CIAC, the Computer Incident Advisory Capability, is the computer
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