-----BEGIN PGP SIGNED MESSAGE----- =============================================================================== Security Advisory CERT-NL =============================================================================== Author/Source : Niels den Otter Index : S-99-26 Distribution : World Page : 1 Classification: External Version: 1 Subject : Windows NT(r) Terminal Servers DOS Vuln. Date : 16-Aug-99 =============================================================================== By courtesy of The U.S. Department of Energy Computer Incident Advisory Capability we received information on a vulnerability in the Windows NT(r) Terminal Server software. The vulnerability could allow an attacker to submit a large number of bogus connection requests and consume all the memory on the Terminal Server. CERT-NL recommends applying the patch described below. ============================================================================== __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Windows NT(r) Terminal Servers DOS Vulnerability August 10, 1999 17:00 GMT Number J-058 ______________________________________________________________________________ PROBLEM: Microsoft has identified a vulnerability that could cause a denial of service threat using the Terminal Server. PLATFORM: Microsoft Windows NT Server 4.0, Terminal Server Edition DAMAGE: The vulnerability could allow an attacker to submit a large number of bogus connection requests and consume all the memory on the Terminal Server. SOLUTION: Apply patches listed below ______________________________________________________________________________ VULNERABILITY Risk is medium. This vulnerability could be exploited ASSESSMENT: remotely if connection requests are not filtered. ______________________________________________________________________________ [ Start Microsoft Advisory ] Microsoft Security Bulletin (MS99-028) - - -------------------------------------- Patch Available for "Terminal Server Connection Request Flooding" Vulnerability Originally Posted: August 09, 1999 Summary ======= Microsoft has released a patch that eliminates a vulnerability that could pose a denial-of-service threat to Microsoft(r) Windows NT(r) Terminal Servers. Frequently asked questions regarding this vulnerability can be found at http://www.microsoft.com/security/bulletins/MS99-028faq.asp Issue ===== When a request to open a new terminal connection is received by a Terminal Server, the server undertakes a resource-intensive series of operations to prepare for the connection. It does this before authenticating the request. This would allow an attacker to mount a denial of service attack by levying a large number of bogus connection requests and consuming all memory on the Terminal Server. This vulnerability could be exploited remotely if connection requests are not filtered. In extreme cases, the server could crash in the face of such an attack; in other cases, normal processing would return when the attack ceased. The patch works by causing the server to require authentication before processing the connection request. Affected Software Versions ========================== - Microsoft Windows NT Server 4.0, Terminal Server Edition Patch Availability ================== - Microsoft Windows NT Server 4.0, Terminal Server Edition: ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes /usa/NT40tse/hotfixes-postSP4/Flood-fix/ NOTE: Line breaks have been added to the above URL for readability. More Information ================ Please see the following references for more information related to this issue. - Microsoft Security Bulletin MS99-028: Frequently Asked Questions, http://www.microsoft.com/security/bulletins/MS99-028faq.asp. - Microsoft Knowledge Base (KB) article Q238600, Multiple Connection Requests Promote Denial of Service Attack, http://support.microsoft.com/support/kb/articles/q238/6/00.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 the ISS X-force (http://www.iss.net) for discovering this vulnerability and working with us to alert customers about it. Revisions ========= - August 09, 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. ******************************************************************* 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/services/bulletin.asp. For security-related information about Microsoft products, please visit the Microsoft Security Advisor web site at http://www.microsoft.com/security. [ End Microsoft Advisory ] ______________________________________________________________________________ CIAC wishes to acknowledge Microsoft for the information contained in this bulletin. ______________________________________________________________________________ ============================================================================== CERT-NL is the Computer Emergency Response Team for SURFnet customers. SURFnet is the Dutch network for educational, research and related institutes. CERT-NL is a member of the Forum of Incident Response and Security Teams (FIRST). 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