Conference minotr::security_advisory

145.0. "Information Only: CIAC H-57, Windows 95/NT" by MINOTR::NOBLE (Your Data, Your Job...Protect Both) Thu May 22 1997 08:15

    The Digital Corporate Information Security Group has received the
    following external security notice.  The impact on DIGITAL internal
    Windows 95 and Windows NT systems is currently being reviewed. Should
    you happen to be a user of Windows 95 or NT, please use due discretion
    before implementing any or all of the solution(s) identified. At this
    time no further recommendation being made.
        
    If you are an internal user of the third party software impacted in
    this notice, and have any questions regarding this notice, then please
    contact your IT Cluster Security Manager.  An up-to-date list can be
    found at URL http://www-is-security.mso.dec.com/
    
                                  -=<>=-
    


           ____________________________________________________________

                       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.

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.