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Microsoft Security Bulletin MS99-015 - Critical

Patch Available for "Malformed Help File" Vulnerability

Published: May 17, 1999 | Updated: March 10, 2003

Version: 2.0

Patch Availability Information Updated: March 10, 2003
Originally Posted: May 17, 1999

Summary

Microsoft has released a patch that eliminates a vulnerability in the Microsoft® Windows NT® help utility. The vulnerability could allow arbitrary code to be run on a Windows NT machine.

A fully supported patch is available to eliminate the vulnerability, and Microsoft recommends that affected customers download and install it, if appropriate.

Issue

The Windows Help utility parses and displays help information for applications. The help information is contained in files of several types that are generated by the Help Compiler (part of the AppWizard utility), and is stored by default in the WINNT\help folder. By default, users can write to this folder. An unchecked buffer exists in the Help utility, and a help file that has been carefully modified could be used to execute arbitrary code on the local machine via a classic buffer overrun technique. Because the Help Compiler's output files do not generate the specific malformation at issue here, this vulnerability could not be accidentally exploited.

The machines primarily at risk from this vulnerability are workstations, terminal servers, and other machines that allow users to log on interactively and add or modify help files. Servers generally do not allow normal users to interactively log on. It is important to note that this vulnerability would affect only the local machine; there is no capability to directly attack a remote machine via this vulnerability.

The patch prevents arbitrary code from being executed on the machine, but does not prevent malformed help files from causing the Help utility to fail. However, failure of the Help utility does not threaten system stability or security, and the Help utility can be restarted without incident.

While there are no reports of customers being adversely affected by this vulnerability, Microsoft is proactively releasing this patch to allow customers to take appropriate action to protect themselves against it.

Affected Software Versions

  • Microsoft Windows NT 4.0

Vulnerability Identifier: CVE-1999-0716

What Microsoft is Doing

Microsoft has released patches that fix the problem identified. The patches are available for download from the sites listed below in What Customers Should Do.

Microsoft also has sent this security bulletin to customers subscribing to the Microsoft Product Security Notification Service. See The Microsoft Product Security Notification Service for more information about this free customer service.

Microsoft has published the following Knowledge Base (KB) article on this issue:

What Customers Should Do

Microsoft highly recommends that customers evaluate the degree of risk that this vulnerability poses to their systems and determine whether to download and install the patch. The patch can be found at:

More Information

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

Obtaining Support on this Issue

If you require technical assistance with this issue, please contact Microsoft Technical Support. For information on contacting Microsoft Technical Support, please see http://support.microsoft.com/contactussupport/?ws=support.

Acknowledgments

Microsoft acknowledges David Litchfield of Arca Systems for discovering this vulnerability and reporting it to us.

Revisions

  • May 17, 1999: Bulletin Created.
  • V2.0 (March 10, 2003): Introduced versioning and updated patch availability information

For additional security-related information about Microsoft products, please visit http://www.microsoft.com/technet/security

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