-----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Malformed UDP Packets in Denial of Service Attacks March 6, 1998 23:00 GMT Number I-031a ______________________________________________________________________________ PROBLEM: Denial of Service attacks on Windows NT and Windows 95 platforms are being seen on the Internet. PLATFORM: Windows 95, Windows NT DAMAGE: Computers freeze or hang, Windows NT machines go to "blue screen of death" immediately or soon after the attack, or spontaneously reboot. SOLUTION: This appears to be the modified teardrop attack (also known as bonk/boink/newtear) described in CIAC Bulletin I-19. Apply the TCP/IP hotfixes provided by Microsoft for Windows NT and Windows 95. ______________________________________________________________________________ VULNERABILITY Unprotected systems crash and lose any unsaved data when this ASSESSMENT: attack occurs. This attack seems to be directed at every or at least many IP address at a targeted site. This attack is widespread. ______________________________________________________________________________ Revision a: Add updated Windows 95 patch. Malformed UDP Packets in Denial of Service Attacks CIAC has information that there have been an ongoing series of denial-of- service attacks directed at whole blocks of IP addresses. The attack uses UDP fragmentation to exploit a known vulnerability on unpatched Windows NT and Windows 95 systems. The attack is a sequence of two UDP packets, the first being the setup packet, and the second, a malformed UDP packet. Because of the way Microsoft implements the TCP/IP stack, processing these UDP packets places the TCP/IP stack in an unstable state. Unprotected Windows NT machines crash and display the "blue screen of death" during or soon after the attack. Windows NT boxes with only SP1 applied seem to reboot. Windows 95 machines hang. The attack is not intentionally damaging to the machines, but as with all such issues can do damage if the machine is accessing the hard drive at the moment the attack occurs. Microsoft has tested these malformed packets and believes the teardrop2 hotfix solves this problem. We suggest patching all machines with this hotfix and the smb/cifs (srv hotfix) which protects against a similar attack. See CIAC Bulletin I-19 for more information on this type of attack and the machines that are vulnerable. Note also that Microsoft has updated and combined the patches for the Teardrop and Land attacks on Windows NT. This patch is now the teardrop2 fix. The teardrop2 hotfix should be used instead of the patches listed in the I-19 Bulletin. We have noted that Windows NT and Windows95 machines that were located behind firewalls did not fail during these attacks. We believe this is due to the fact that most firewalls automatically drop malformed UDP packets. To get more information from Microsoft Corporation about these attacks, see the "Update on Network Denial of Service Attacks" at: http://www.microsoft.com/security/netdos.htm hotfixes for NT 4: - ------------------ ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40/hotfixes- postSP3/ teardrop2-fix srv-fix hotfixes for NT 3.5: - -------------------- ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT351/hotfixes- postSP5/ teardrop2-fix srv-fix hotfixes for Windows 95: - ------------------------ Windows 95 without Winsock installed is not vulnerable. All other versions of Windows 95 should update to Winsock 2. Microsoft has released an update called the "Winsock 2 update" for Windows 95. According to Microsoft, this update contains fixes for all known vulnerabilities in the Windows 95 TCP/IP stack. Microsoft is updating their security advisories to recommend that all Windows 95 customers who are concerned about TCP/IP security and denial of service issues should upgrade to WinSock 2 using this update. This update works for all existing Windows 95 systems, and can be installed on top of systems that already have existing security updates installed. This update is available from www.microsoft.com/windows95/info/ws2.htm We have also been advised that Windows 98 RC0 (release candidate 0) contains all known TCP/IP updates, and is not vulnerable to this attack. Warning: These are hotfixes from Microsoft that are not as well tested as a Service Pack. Be sure to follow the directions for installing the patches or you may make your machine unbootable. The Service Pack 3 for NT 4 is required before installing any of the hotfixes noted above. If you reinstall Service Pack 3, you must reinstall the hotfixes. We have installed all the hotfixes for Windows NT 4 and Windows 95 and have not experienced any problems. Windows NT users should turn on the creation of a crash dump file. To do this, select Settings on the Task Menu from the Start button, select Control Panel, then the System icon, and in the System Properties window select the "Write debugging information to" checkbox. If a machine with the teardrop2 fix installed is attacked and crashes, please inform your Computer Security Department and give them information about which patches were applied. The crash dump file may be requested by Microsoft. _____________________________________________________________________________ CIAC wishes to acknowledge the many contributions from Computer Security Managers who helped to capture UDP packets and provide us with valuable information. We would also like to thank Microsoft Corporation for their significant contributions. _____________________________________________________________________________ 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: +1 510-422-8193 FAX: +1 510-423-8002 STU-III: +1 510-423-2604 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 510-422-8193 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 (510) 423-4753 (28.8K baud) +1 (510) 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-021 "smurf" IP Denial-of-Service Attackts I-022: IBM AIX "routed" daemon Vulnerability I-023: Macro Virus Update I-024: CGI Security Hole in EWS1.1 Vulnerability I-025: Windows NT based Web Servers File Access Vulnerability I-026: Vulnerability in ssh-agent I-027: HP-UX Vulnerabilities (CUE, CDE, land) I-028: Vulnerabilities in CDE I-029: IBM AIX Telnet Denial-of-Service Vulnerability I-030: SunOS volrmmount (1) Vulnerability -----BEGIN PGP SIGNATURE----- Version: 4.0 Business Edition iQCVAwUBNQChz7nzJzdsy3QZAQFVQwQAkjlzPREO5+3FFpyMZ6f0W5n5zADvV96w tvczRcKdhDE29fCaJkhRtadh1ePrDMJRjKo7qqGl2oIjUQopTLxaS+DLYveAzFil NE3RHNkeg2vJGLSlmjoCLxbrk18eQp1ctgbUbjPUHqptdAUjX38bw+Uu2jKJpLUr v+ozHKt/Su4= =aZJA -----END PGP SIGNATURE-----