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____________________________________________________________
The U.S. Department of Energy
Computer Incident Advisory Capability
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INFORMATION BULLETIN
Windows NT/95 Out of Band Data Exploit
May 14, 1997 18:00 GMT Number H-57
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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.
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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 -
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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
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You will receive an acknowledgment email immediately with a confirmation
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If you include the word 'help' in the body of an email to the above address,
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get past issues of CIAC bulletins via email, etc.
PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing
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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
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