From secnotif@MICROSOFT.COM Wed Jun 23 21:52:25 1999 From: Microsoft Product Security To: MICROSOFT_SECURITY@ANNOUNCE.MICROSOFT.COM Date: Wed, 23 Jun 1999 12:28:32 -0700 Subject: Microsoft Security Bulletin (MS99-021) The following is a Security Bulletin from the Microsoft Product Security Notification Service. Please do not reply to this message, as it was sent from an unattended mailbox. ******************************** Microsoft Security Bulletin (MS99-021) -------------------------------------- Patch Available for "CSRSS Worker Thread Exhaustion" Vulnerability Originally Posted: June 23, 1999 Summary ======= Microsoft has released a patch that eliminates a vulnerability in the Microsoft(r) Windows NT(r) 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, its background, and the patch can be found at http://www.microsoft.com/security/bulletins/ms99-021faq.asp 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 Patch Availability ================== The patch is available at ftp://ftp.microsoft.com/bussys/winnt/ winnt-public/fixes/usa/nt40/Hotfixes-PostSP5/CSRSS-fix/ NOTE: A line break has been inserted into the above URL for readability. More Information ================ Please see the following references for more information related to this issue. - Microsoft Security Bulletin MS99-021: Frequently Asked Questions, http://support.microsoft.com/support/bulletins/ms99-021faq.asp. - Microsoft Knowledge Base (KB) article Q2133323, "Exceeding MaxRequestThreads may Cause Windows NT to Hang", http://support.microsoft.com/support/kb/articles/q231/3/23.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 Jeff Sumner for discovering this vulnerability and reporting it. Revisions ========= - June 23, 1999: Bulletin Created. --------------------------------------------------------------------- THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. (c) 1999 Microsoft Corporation. All rights reserved. Terms of Use. ******************************************************************* You have received this e-mail bulletin as a result of your registration to the Microsoft Product Security Notification Service. You may unsubscribe from this e-mail notification service at any time by sending an e-mail to MICROSOFT_SECURITY-SIGNOFF-REQUEST@ANNOUNCE.MICROSOFT.COM The subject line and message body are not used in processing the request, and can be anything you like. For more information on the Microsoft Security Notification Service please visit http://www.microsoft.com/security/bulletin.htm. For security-related information about Microsoft products, please visit the Microsoft Security Advisor web site at http://www.microsoft.com/security.