Microsoft Security Bulletin (MS99-043)

Patch Available for "Javascript Redirect" Vulnerability 
Originally Posted: October 18, 1999
Re-released: November 17, 1999 

Summary
On October 18, 1999, Microsoft released the original version of this bulletin, in order to advise customers of a workaround for a vulnerability in Microsoft® 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/MS99-043faq.asp. 

Issue
Client-local data that is displayed in the browser window can be made available to the server by using a redirect to a Javascript applet running in the same window. This in effect bypasses cross-domain security and makes the data available to the applet, which could then send the data to a hostile server. 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. 

Affected Software Versions


Microsoft Internet Explorer 4.01 and 5. 

Patch Availability


http://www.microsoft.com/downloads 
http://www.microsoft.com/msdownload/iebuild/jsredir/en/jsredir.htm 
NOTE: The IE 4.01 patch requires IE 4.01 SP2 in order to install. IE 4.01 SP 2 is available at http://www.microsoft.com/Windows/ie/download/windows.htm. 
NOTE: The patch will be available shortly via the WindowsUpdate site. When this happens, we will modify this bulletin to provide additional information. 

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

Microsoft Security Bulletin MS99-043: Frequently Asked Questions, http://www.microsoft.com/security/bulletins/MS99-043faq.asp. 
Microsoft Knowledge Base (KB) article Q244356, Update for "Javascript Redirect" Vulnerability in Internet Explorer 4.01, http://support.microsoft.com/support/kb/articles/q244/3/56.asp.

Microsoft Knowledge Base (KB) article Q244357, Update for "Javascript Redirect" Vulnerability in Internet Explorer 5, http://support.microsoft.com/support/kb/articles/q244/3/57.asp.

Microsoft Security Advisor web site, http://www.microsoft.com/security/default.asp. 
NOTE: It may take 24 hours from the original posting of this bulletin for the KB articles to be visible. 

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. 

Revisions


October 18, 1999: Bulletin Created. 
November 17, 1999: Bulletin re-released to provide information on availability of patch.