__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Microsoft "Malformed Request to Domain Controller" February 23, 2001 19:00 GMT Number L-049 ______________________________________________________________________________ PROBLEM: A core service running only on Windows 2000 domain controllers has a software flaw. This flaw affects system handling of invalid service requests. PLATFORM: Windows 2000 Server, Advanced Server and Datacenter Server DAMAGE: The sending of invalid service requests to a server consumes CPU cycles. A stream of invalid service requests could significantly slow the CPU, resulting in a denial of service (DoS) to server resources. SOLUTION: Microsoft recomends that all customers apply the patch. ______________________________________________________________________________ VULNERABILITY The risk is LOW. There are mitigating circumstances, as stated ASSESSMENT: in the Microsoft bulletin. ______________________________________________________________________________ [****** Begin Microsoft Bulletin ******] - ---------------------------------------------------------------------- Title: Malformed Request to Domain Controller can Cause Denial of Service Date: 20 February 2001 Software: Windows 2000 Server, Advanced Server and Datacenter Server Impact: Denial of Service Bulletin: MS01-011 Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS01-011.asp. - ---------------------------------------------------------------------- Issue: ====== A core service running on all Windows 2000 domain controllers (but not on any other machines) contains a flaw affecting how it processes a certain type of invalid service request. Specifically, the service should handle the request at issue here by determining that it is invalid and simply dropping it; in fact, the service performs some resource-intensive processing and then sends a response. If an attacker sent a continuous stream of such requests to an affected machine, it could consume most or all of the machine's CPU availability. This could cause the domain controller to process requests for service slowly or not at all, and could limit the number of new logons the machine could process and the number of Kerberos tickets that could be issued. Mitigating Factors: ==================== - The machine would automatically resume normal processing as soon as the stream of requests ceased. - Although the attacker could, in theory, use the vulnerability to completely deny service to network users, in practice the attack rarely consumes more than 75% of the available CPU resources. - Users who were already logged on and were using previously issued Kerberos tickets would not be affected by domain controller unavailability. - If there were multiple domain controllers on the domain, the unaffected machines could pick up the other machine's load. - If normal security practices have been followed, Internet users would be prevented by firewalling and other measures from levying requests directly to domain controllers. Patch Availability: =================== - A patch is available to fix this vulnerability. Please read the Security Bulletin http://www.microsoft.com/technet/security/bulletin/ms01-011.asp for information on obtaining this patch. - --------------------------------------------------------------------- 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. [****** End Microsoft Bulletin ******] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of Microsoft for the information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 (7x24) FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@ciac.org Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ (or http://ciac.llnl.gov -- they're the same machine) Anonymous FTP: ftp.ciac.org (or ciac.llnl.gov -- they're the same machine) PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. 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