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Microsoft Security Bulletin MS99-026 - Critical

Patch Available for "Malformed Dialer Entry" Vulnerability

Published: July 29, 1999 | Updated: March 21, 2003

Version: 2.0

Patch Availability Information Updated: March 21, 2003
Originally Posted: July 29, 1999

Summary

Microsoft has released a patch that eliminates a security vulnerability in the Phone Dialer accessory in Microsoft® Windows NT®. The vulnerability could be used to run arbitrary code in a user's security context on Windows NT systems.

Frequently asked questions regarding this vulnerability can be found at http://www.microsoft.com/technet/security/bulletin/fq99-026.mspx

Issue

Dialer.exe has an unchecked buffer in the portion of the program that processes the dialer.ini file. This vulnerability could be used to run arbitrary code via a classic buffer overrun technique.

The circumstances of this vulnerability require a fairly complicated attack scenario that limits its scope. Dialer.exe runs in the security context of the user, so it would not benefit an attacker to simply modify a dialer.ini file and run it, as he or she would not gain additional privileges. Instead, the attacker would need to modify the dialer.ini file of another user who had higher privileges, then wait for that user to run Dialer.

Although the unchecked buffer is present in all versions of Windows NT 4.0, the attack scenario would result in workstations that have dial-out capability being chiefly at risk. The FAQ discusses this in greater detail.

Affected Software Versions

  • Microsoft Windows NT Workstation 4.0
  • Microsoft Windows NT Server 4.0
  • Microsoft Windows NT Server 4.0, Enterprise Edition
  • Microsoft Windows NT Server 4.0, Terminal Server Edition

Vulnerability Identifier: CVE-1999-0700

Patch Availability

Windows NT Server 4.0, Terminal Server Edition: http://www.microsoft.com/technet/security/patchavailability.mspx

More Information

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

Microsoft Security Bulletin MS99-026: Frequently Asked Questions, http://www.microsoft.com/technet/security/bulletin/fq99-026.mspx.

Microsoft Knowledge Base (KB) article 237185, Dialer.exe Access Violation with Phone Entry more than 128 Bytes, http://support.microsoft.com/default.aspx?scid=kb;en-us;237185&sd=tech.

(Note It may take 24 hours from the original posting of this bulletin for the KB article to be visible; however, a copy will be immediately available in the patch folder.)

Obtaining Support on this Issue

This is a fully supported patch. Information on contacting Microsoft Technical Support is available at 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

  • July 29, 1999: Bulletin Created.
  • V2.0 (March 21, 2003): Introduced versioning and updated patch availability information.

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