• Article

Security Bulletin

Microsoft Security Bulletin MS99-021 - Important

Patch Available for "CSRSS Worker Thread Exhaustion" Vulnerability

Published: June 23, 1999 | Updated: March 10, 2003

Version: 2.0

Patch Availability Information Updated: March 10, 2003

Originally Posted: June 23, 1999

Summary

Microsoft has released a patch that eliminates a vulnerability in the Microsoft® Windows NT® CSRSS process that could be used to create a denial of service condition against a machine that allows interactive logons.

Frequently asked questions regarding this vulnerability can be found at https://www.microsoft.com/technet/security/bulletin/fq99-021.mspx

Issue

If all worker threads in CSRSS.EXE are occupied awaiting user input, no other requests can be serviced, effectively causing the server to hang. When user input is provided, processing returns to normal. The patch eliminates the vulnerability by ensuring that the last CSRSS worker thread services only requests that do not require user input.

Affected Software Versions

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

Vulnerability Identifier: CVE-1999-0723

Patch Availability

The patch is available at https:

More Information

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

  • Frequently Asked Questions: Microsoft Security Bulletin MS99-021, https://www.microsoft.com/technet/security/bulletin/fq99-021.mspx.

  • Microsoft Knowledge Base (KB) article 233323, Exceeding MaxRequestThreads may Cause Windows NT to Hang, </https:>https:.

    (Note It may take 24 hours from the original posting of this bulletin for the KB article to be visible.)

  • Microsoft Security web site, </https:>https:.

Obtaining Support on this Issue

This is a fully supported patch. Information on contacting Microsoft Technical Support is available at </https:>https:.

Acknowledgments

Microsoft acknowledges Jeff Sumner for discovering this vulnerability and reporting it.

Revisions

  • June 23, 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 https://www.microsoft.com/technet/security

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