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Q192292: Unpredictable TCP Sequence Numbers in SP4

Article: Q192292
Product(s): Microsoft Windows NT
Version(s): winnt:4.0,4.0a
Operating System(s): 
Keyword(s): kbFEA kbWinNT400sp4fea
Last Modified: 09-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Server version 4.0 
- Microsoft Windows NT Workstation version 4.0 
- Microsoft Windows NT Server, Enterprise Edition version 4.0 
- Microsoft Windows NT Server version 4.0, Terminal Server Edition 
- Microsoft BackOffice Small Business Server versions 4.0, 4.0a 
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SYMPTOMS
========

The TCP protocol assigns an initial sequence number to each connection. Prior to
Service Pack 4, it is possible, through careful analysis, to determine the
initial TCP sequence number for a specific Windows NT communications session. By
predicting a TCP session's sequence number, it could be possible to disrupt the
integrity of a communication session that does not provide its own session
integrity. This is often referred to as "connection hijacking."

In Service Pack 4, the method of assigning sequence numbers to TCP session has
changed to make them more unpredictable.

RESOLUTION
==========

To resolve this problem, obtain the latest service pack for Windows NT version
4.0. For more information, please see the following article in the Microsoft
Knowledge Base.

  Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack


STATUS
======

Microsoft has confirmed this to be a problem in Windows NT version 4.0. This
problem was first corrected in Windows NT 4.0 Service Pack 4.

Additional query words: security hijacking hijack tcp port connect connections ISN SYN

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Keywords          : kbFEA kbWinNT400sp4fea 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400 kbWinNTS400search kbWinNTS400 kbNTTermServ400 kbNTTermServSearch kbAudDeveloper kbSBServSearch kbSBServ400 kbSBServ400a
Version           : winnt:4.0,4.0a
Hardware          : ALPHA x86
Issue type        : kbbug
Solution Type     : kbfix

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