-----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Windows NT RPC Spoofing Denial of Service Vulnerability October 2, 1998 21:00 GMT Number J-001 ______________________________________________________________________________ PROBLEM: A vulnerability exist in the way that Windows NT processes bad Remote Procedure Call (RPC) datagrams. PLATFORM: Microsoft Windows NT Workstation version 4.0 Microsoft Windows NT Server version 4.0 Microsoft Windows NT Server version 4.0, Terminal Server Edition DAMAGE: If exploited, an attacker could send an RPC datagram to a machine and spoof the return address so that the datagram appears to have come from another machine. This tricks the two servers into erroneously sending RPC error messages to each other continuously. SOLUTION: Apply available patches. ______________________________________________________________________________ VULNERABILITY Risk is low. While there have not been any reports of customers ASSESSMENT: being adversely affected by these problems, Microsoft is releasing a patch to address any risks posed by this issue. ______________________________________________________________________________ [ Start Microsoft Advisory ] Microsoft Security Bulletin (MS98-014) Update available for RPC Spoofing Denial of Service on Windows NT Originally Posted: September 29, 1998 Last Revised: September 29, 1998 Summary Microsoft has released a patch that enhances the way that Windows NT processes bad Remote Procedure Call (RPC) datagrams. This patch prevents a malicious attack in which an attacker sends an RPC datagram to a server and spoofs the return address so that the datagram appears to have come from another server. This tricks the two servers into erroneously sending RPC error messages to each other. These error messages could cause a temporary loop resulting in high CPU utilization and network bandwidth until the bad packets are discarded. Customers using affected software listed below should evaluate risks to their systems posed by this issue, then download and apply this patch as appropriate to their configurations. Issue It is possible for a malicious attacker to send spoofed RPC datagrams to UDP destination port 135 so that it appears as if one RPC server sent bad data to another RPC server. The second server returns a REJECT packet and the first server (the spoofed server) replies with another REJECT packet creating a loop that is not broken until a packet is dropped, which could take a few minutes. If this spoofed UDP packet is sent to multiple computers, a loop could possibly be created, consuming processor resources and network bandwidth. While there have not been any reports of customers being adversely affected by these problems, Microsoft is releasing a patch to address any risks posed by this issue. Affected Software Versions The following software is affected by this vulnerability: * Microsoft Windows NT Workstation version 4.0 * Microsoft Windows NT Server version 4.0 * Microsoft Windows NT Server version 4.0, Terminal Server Edition What Microsoft is Doing On September 29th Microsoft released a patch that changes the behavior of the RPC service so it can better detect spoofed packets and not respond to them, preventing an attack of this type from causing any problem. Microsoft has sent this security bulletin to customers subscribing to the Microsoft Product Security Notification Service (see http://www.microsoft.com/security/bulletin.htm for more information about this free customer service). Microsoft has published the following Knowledge Base (KB) articles on this issue: * Microsoft Knowledge Base (KB) article Q193233, RPCSS.EXE Consumes 100% CPU due to RPC-spoofing Attack http://support.microsoft.com/support/kb/articles/q193/2/33.asp (Note: It might take 24 hours for the KB article to be visible in the Web- based Knowledge Base. A copy of the article is also available on the FTP server in the same directory as the fix.) What customers should do Microsoft recommends that customers using affected software listed above should evaluate risks to their systems posed by this issue, then download and apply this patch as appropriate to their configuration. Fix for Windows NT 4.0 x86 version - * ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40/hotfixes- postSP3/snk-fix/snk-fixi.exe Fix for Windows NT 4.0 Alpha version - * ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40/hotfixes- postSP3/snk-fix/snk-fixa.exe Fix for Windows NT Server 4.0, Terminal Server Edition - This fix will be available shortly. It will be available in the following location: * ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/ NT40TSE/hotfixes-postSP3/Snk-fix/ Additional Details The following are additional notes about this issue: * It is relatively easy to detect a malicious attack of this kind by using a network analyzer to watch for bad RPC packets. Also, during an attack, the RPCSS.EXE service will consume a very large amount of CPU cycles (during an active, on-going attack, it will consume 100% of CPU cycles.) * Systems that are currently in an error loop (sending error messages back and forth) will recover by themselves shortly after the attacker has stopped sending spoofed packets. * If two systems are currently in an error loop (sending error messages back and forth) momentarily disconnecting one system from the network will cause an end to that loop, since UDP packets are connectionless. * These error packets are addressed to UDP port 135 and can be filtered at a corporate firewall to protect against external attackers. More Information Please see the following references for more information related to this issue. * Microsoft Security Bulletin MS98-014, Update available for RPC Spoofing Denial of Service on Windows NT, (the Web posted version of this bulletin), http://www.microsoft.com/security/bulletins/ms98-014.htm * Microsoft Knowledge Base (KB) article Q193233, RPCSS.EXE Consumes 100% CPU due to RPC-spoofing Attack http://support.microsoft.com/support/kb/articles/q193/2/33.asp (Note: It might take 24 hours for the KB article to be visible in the Web- based Knowledge Base. A copy of the article is also available on the FTP server in the same directory as the fix.) Acknowledgements Microsoft wishes to acknowledge the contributions of Internet Security Systems, Inc. (http://www.iss.net) for reporting this problem to us. Revisions September 29, 1998: Bulletin Created For additional security-related information about Microsoft products, please visit http://www.microsoft.com/security 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 Advisory ] ______________________________________________________________________________ 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 FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@llnl.gov For emergencies and off-hour assistance, DOE, DOE contractor sites, and the NIH may contact CIAC 24-hours a day. During off hours (5PM - 8AM PST), call the CIAC voice number 925-422-8193 and leave a message, or call 800-759-7243 (800-SKY-PAGE) to send a Sky Page. CIAC has two Sky Page PIN numbers, the primary PIN number, 8550070, is for the CIAC duty person, and the secondary PIN number, 8550074 is for the CIAC Project Leader. 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) Modem access: +1 (925) 423-4753 (28.8K baud) +1 (925) 423-3331 (28.8K baud) CIAC has several self-subscribing mailing lists for electronic publications: 1. CIAC-BULLETIN for Advisories, highest priority - time critical information and Bulletins, important computer security information; 2. SPI-ANNOUNCE for official news about Security Profile Inspector (SPI) software updates, new features, distribution and availability; 3. SPI-NOTES, for discussion of problems and solutions regarding the use of SPI products. Our mailing lists are managed by a public domain software package called Majordomo, which ignores E-mail header subject lines. To subscribe (add yourself) to one of our mailing lists, send the following request as the E-mail message body, substituting ciac-bulletin, spi-announce OR spi-notes for list-name: E-mail to ciac-listproc@llnl.gov or majordomo@tholia.llnl.gov: subscribe list-name e.g., subscribe ciac-bulletin You will receive an acknowledgment email immediately with a confirmation that you will need to mail back to the addresses above, as per the instructions in the email. This is a partial protection to make sure you are really the one who asked to be signed up for the list in question. If you include the word 'help' in the body of an email to the above address, it will also send back an information file on how to subscribe/unsubscribe, get past issues of CIAC bulletins via email, etc. 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. LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) I-083: Eudora Pro E-Mail Attachment Vulnerability I-084: Cisco IOS Remote Router Crash I-085: Microsoft IE Upgrade Trojan Horse Program I-086: Cisco CRM Temporary File Vulnerability I-087: Microsoft PPTP Security Vulnerabilities I-088: NFS clients rpc.pcnfsd Vulnerability I-089: SGI Seyon Security Vulnerability I-090: HP-UX dtmail/rpc.ttdbserverd Vulnerability I-091: Stack Overflow in ToolTalk RPC Service I-092: Ping Buffer Overflow Vulnerability -----BEGIN PGP SIGNATURE----- Version: 4.0 Business Edition iQCVAwUBNhlJKrnzJzdsy3QZAQEVGAP+OsgkKgxmZXfXA/7LNnxDo3jCmM1zru4z G/dU79JeqUA9raFCvat5FFHfO2WOnDhi3JY5ZXagt0zgdsZuFQtQbayClPYqHW4Q ZisQtDlX4oBKYKVNRr8w1AbZqZZLoISFT1dajNnoYacyYVeYLZ0TE6DGCHuzm58I us5z0+fFj/4= =52Xa -----END PGP SIGNATURE-----