Microsoft Security Bulletin (MS99-048)

Patch Available for "Active Setup Control" Vulnerability 
Originally Posted: November 11, 1999


Summary
Microsoft has released a patch that eliminates a vulnerability that could allow a malicious user to embed an unsafe executable within an email and disguise it as a safe type of attachment. Through a complicated series of steps, the unsafe executable could be made to execute under certain conditions, if the user opened the attachment. 

Frequently asked questions regarding this vulnerability can be found at http://www.microsoft.com/security/bulletins/MS99-048faq.asp. 

Issue
A particular ActiveX control allows cabinet files to be launched and executed. This could allow an HTML mail to contain a malicious cabinet file, disguised as a file of an innocuous type. If a user attempted to open this file, the operation would fail but could, depending on the mail package, leave a copy of the file in a known location. The ActiveX control could then be used via a script embedded in the mail to launch the copy, thereby executing the malicious code. 

The vulnerability could only be exploited in cases where a mail reader were used that allowed scripts in HTML mail and stored temporary copies of launched programs in known locations. The patch restricts the ability of the control to launch unsigned cabinet files that have been downloaded from the local machine. 

Affected Software Versions


The affected ActiveX control ships as part of Microsoft Internet Explorer 4 and 5 

Patch Availability


http://windowsupdate.microsoft.com 
http://www.microsoft.com/msdownload 
http://www.microsoft.com/msdownload/iebuild/ascontrol/en/ascontrol.htm 
NOTE: Microsoft produces security patches for Internet Explorer 4.01 SP2 and higher. In the event that this package is applied to Internet Explorer 4.01 SP1, the package states that a fix is not needed. This message is incorrect, as the vulnerability does exist on Internet Explorer 4.01 SP1 or any earlier release. If you are using Internet Explorer 4.01 SP1 or any earlier release, please upgrade to the latest version of Internet Explorer to resolve this issue. 

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

Microsoft Security Bulletin MS99-048: Frequently Asked Questions, http://www.microsoft.com/security/bulletins/MS99-048faq.asp. 
Microsoft Knowledge Base (KB) article Q244540, Update Available for "Active Setup Control" Vulnerability, http://support.microsoft.com/support/kb/articles/q244/5/40.asp
(Note: It may take 24 hours from the original posting of this bulletin for the 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 Juan Carlos Garcia Cuartango of Spain for bringing this issue to our attention. 

Revisions


November 11, 1999: Bulletin Created.