-----BEGIN PGP SIGNED MESSAGE----- ____________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Windows NT/95 Out of Band Data Exploit May 14, 1997 18:00 GMT Number H-57 ______________________________________________________________________________ PROBLEM: Windows systems are vulnerable to denial-of-service attack PLATFORM: Windows NT (server and workstation versions up through 4.0) Windows 95, Windows for Workgroups 3.11. DAMAGE: Windows NT: Causes a system crash. Unsaved data is lost. Windows 95, Windows for Workgroups: Causes most open applications to crash, unsaved data is lost. SOLUTION: Apply the countermeasures described below for firewall configuration and local Microsoft patch. ******Make sure correct service packs are installed! ****** Installing the Microsoft patches without correct service packs will render your system unbootable!!! ______________________________________________________________________________ VULNERABILITY Code and exploit are widely available, and can be run remotely ASSESSMENT: over a network. ______________________________________________________________________________ Introduction: An executable code which exploits a Windows' Out-of-Band data assumption has been released on the Internet. When a Windows system receives a packet with the "URGENT" flag set, it expects data will follow that flag. The exploit consists of setting the URGENT flag, but not following it with data. The port most susceptible is TCP Port 139, the Netbios Session Service port. Although port 139 is the most commonly attacked port, there is potential for successful attacks on other ports as well. This attack is effective remotely or locally (it also works on the machine it's executing from). Windows NT: When Windows NT is successfully attacked, it crashes. The system displays the "blue screen of death", and is not respondent. Except for losing the contents of unsaved documents and files, there are no long-lasting effects from this attack. Windows 95, Windows for Workgroups 3.11: When Windows for Workgroups or Windows 95 is successfully attacked, an application exception screen will be displayed. This is a blue screen alerting the user that an application is not responding. Any unsaved data will be lost, however there are no other long-lasting effects from this attack. Solution: If your Windows NT system has been successfully attacked, it must be rebooted. The system operates normally once the system is rebooted. If your Windows for Workgroups or Windows 95 system has been successfully attacked, follow the instructions on the Application exception screen to close the applications not responding and return to the desktop. The system will operate normally once you have returned to the desktop. A reboot is not required, but recommended. Prevention: The best and most conservative measure for preventing this and similar attacks is to have a strong firewall in place. The firewall can be configured to choose and authorize trusted hosts to enter through the firewall. Additionally, this specific exploit can be prevented by disabling Netbios services through firewalls/routers. (Be aware that some versions of the exploit have the potential to choose ports, and therefore may successfully attack other ports). Since changing the firewall configuration is not always feasible in a network environment, there is a "local" patch provided by Microsoft for Windows NT systems. This patch updates the Tcpip.sys file, which contains the TCP/IP Driver. Microsoft plans to include the patch in the next Service Pack and therefore does not recommend applying the patch unless you are severely impacted by this problem. If you still need to apply this patch, update your Emergency Repair Disk first, as the patches have not been regression tested and therefore may not work as described. ********************************************************************* ***** MAKE SURE THE CORRECT SERVICE PACKS ARE INSTALLED!!!!! ***** ***** INSTALLING THIS FIX WITHOUT THE CORRECT SERVICE PACKS ***** ***** WILL RENDER YOUR SYSTEM UNBOOTABLE!!!!!! ***** ********************************************************************* Microsoft's patch locations: Windows NT 4.0: ****SERVICE PACK 2 MUST BE INSTALLED**** ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40/hotfixes- postSP2/oob-fix Read the text files, Q143478.txt and Readme.txt, in the directory and follow instructions. Windows NT 3.51: *****SERVICE PACK 5 MUST BE INSTALLED**** ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT351/hotfixes- postSP5/oob-fix Read the text files, Q143478.txt and Readme.txt, in the directory and follow instructions. _____________________________________________________________________ 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://ciac.llnl.gov/ Anonymous FTP: ciac.llnl.gov (128.115.19.53) 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. CIAC-NOTES for Notes, a collection of computer security articles; 3. SPI-ANNOUNCE for official news about Security Profile Inspector (SPI) software updates, new features, distribution and availability; 4. 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, ciac-notes, 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-notes 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) H-49: NLS Buffer Overflow Vulnerability H-22a: talkd Buffer Overrun Vulnerability H-29a: HP-UX sendmail Patches Vulnerability H-50: HP-UX SYN Flood and libXt patches H-51: Vulnerability in libXt H-52: IRIX csetup Program Vulnerability H-53: Vulnerability in webdist.cgi H-54: Vulnerability in xlock H-55: IRIX netprint Program Security Vulnerability H-56: Solaris 2.x lp temporary files creation Vulnerability -----BEGIN PGP SIGNATURE----- Version: 4.0 Business Edition iQCVAwUBM3yAm7nzJzdsy3QZAQEzQwQA84laEQ+0zN8mxya8FzZhjB3s4Qf23CHt CxXv/I/3Ii0+YNn8Yh/Vw/51G7aapMTKiS7q/kHohgyO6pHYP+Aasma5VtONH6GM fEZdl4FWRStdfvHzDBO0l7s/daxYJXWX+ZDYwULyv+S0XgDTFLg7uWLFCLIb78MB xf8FHSzLfug= =xked -----END PGP SIGNATURE-----