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Secure Networks Inc.
Security Advisory
February 14, 1998
Windows NT Logon Denial of Service
This advisory addresses a denial of service attack which can be launched
against Microsoft Windows NT servers. When launched, this attack results
in a "Blue Screen", causing the Windows NT system to reboot. This
vulnerability affects Windows NT systems, including systems which have
installed Service Pack 3 and all hotfixes.
Problem Description
~~~~~~~~~~~~~~~~~~~
Windows NT utilizes the SMB/CIFS protocol for network file sharing and
other communications. To access the SMB/CIFS service on a Windows NT
system, a logon request is initiated. Due to incorrect processing of
the SMB logon packet, memory corruption occurs within the Windows NT
kernel. As a result of corruption, a "Blue Screen" occurs, and the
system reboots, and in some instances hangs on this screen.
This attack can be launched without a valid login and password, since
corruption occurs during processing of the logon request.
Technical Details
~~~~~~~~~~~~~~~~~
An SMB logon packet contains the following data:
- Username
- Password
- Operating system
- Lan Manager type
- Domain
The SMB logon request contains the size of data which follows. When the
size of data which is specified in the request does not correspond to the
size of data which is actually present, corruption occurs.
Impact
~~~~~~
Malicious users can launch denial of service attacks against Microsoft
Windows NT systems.
Vulnerable Systems
~~~~~~~~~~~~~~~~~~
Systems which have shown to be vulnerable to this attack include the
following:
- Windows NT 4.0
- Windows NT 4.0 with SP3 installed
- Windows NT 4.0 with SP3 and hotfixes installed
Fix Information
~~~~~~~~~~~~~~~
Microsoft has issued a patch for Windows NT to solve this problem at
the following location:
ftp site : ftp.microsoft.com
directory: /bussys/winnt/winnt-public/fixes/usa/NT40/hotfixes-postSP3/srv-fix
Additional Information
~~~~~~~~~~~~~~~~~~~~~~
To the best of our knowledge no program to exploit this problem has been
made publicly availible.
For additional information see Microsoft Knowledge Base article Q180963.
This problem was discovered by Oliver Friedrichs <oliver@securenetworks.com>
You can browse our web site at http://www.secnet.com
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You can find Secure Networks papers at ftp://ftp.secnet.com/pub/papers
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You can contact Secure Networks Inc. at <sni@secnet.com> using
the following PGP key:
Type Bits/KeyID Date User ID
pub 1024/9E55000D 1997/01/13 Secure Networks Inc. <sni@secnet.com>
Secure Networks <security@secnet.com>
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Copyright Notice
~~~~~~~~~~~~~~~~
The contents of this advisory are Copyright (C) 1998 Secure Networks Inc,
and may be distributed freely provided that no fee is charged for
distribution, and that proper credit is given.
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