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Microsoft Security Bulletin MS99-040 - Important

Patch Available for "Download Behavior" Vulnerability

Published: September 28, 1999 | Updated: October 12, 1999

Version: 1.2

Originally Posted: September 28, 1999
Updated: October 08, 1999
Revised: October 12, 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® 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/technet/security/bulletin/fq99-040.mspx.

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

Vulnerability Identifier: CVE-1999-0891

Patch Availability

The patch is available at the following locations:

More Information

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

Obtaining Support on this Issue

Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/contactussupport/?ws=support.

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.
  • October 12, 1999: Updated to provide information on availability of patch via WindowsUpdate.

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