Microsoft Security Bulletin (MS99-046)

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Microsoft Security Bulletin (MS99-046)
--------------------------------------

Patch Available to Improve TCP Initial Sequence Number Randomness
Originally Posted: October 22, 1999

Summary
=======
Microsoft has released a patch that significantly improves the randomness of
the TCP initial  sequence numbers (ISNs) generated by the TCP/IP stack in
Microsoft(r) Windows NT(r) 4.0.  Improving the randomness of ISNs eliminates
a class of potential attacks against Windows NT 4.0  systems.

Frequently asked questions regarding this vulnerability can be found
at http://www.microsoft.com/security/bulletins/MS99-046faq.asp.

Issue
=====
The ISNs used in TCP/IP sessions should be as random as possible in order to
prevent attacks such  as IP address spoofing and session hijacking. This
patch improves the randomness of the Windows  NT 4.0 TCP/IP ISN generation,
providing 15 bits of entropy.

Affected Software Versions
==========================
 - Microsoft Windows NT 4.0 Workstation
 - Microsoft Windows NT 4.0 Server
 - Microsoft Windows NT 4.0 Server, Enterprise Edition
 - Microsoft Windows NT 4.0 Server, Terminal Server Edition

Patch Availability
==================
 - x86:
   http://download.microsoft.com/download/winntsrv40/patch/
   4.0.1381.7014/nt4/en-us/q243835.exe
 - Alpha:
   http://download.microsoft.com/download/winntsrv40/patch/
   4.0.1381.7014/alpha/en-us/q243835.exe

NOTE: Line breaks have been inserted into the above URLs for readability.

More Information
================
Please see the following references for more information related to this
issue.
 - Microsoft Security Bulletin MS99-046: Frequently Asked Questions,
   http://www.microsoft.com/security/bulletins/MS99-046faq.asp.
 - Microsoft Knowledge Base (KB) article Q243835,
   How to Prevent Predictable TCP/IP Initial Sequence Numbers,
   http://support.microsoft.com/support/kb/articles/q243/8/35.asp.
   (Note: It may take 24 hours from the original posting of this
   bulletin for this KB article to be visible.)
 - CERT Advisory CA-95.01,
   Topic: IP Spoofing Attacks and Hijacked Terminal Connections,
   http://www.cert.org/advisories/
   CA-95.01.IP.spoofing.attacks.and.hijacked.terminal.connections.html.
   (Note: A line break has been inserted into the above URL for readability)
 - Microsoft Security Advisor web site,
   http://www.microsoft.com/security/default.asp.

Obtaining Support on this Issue
===============================
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
http://support.microsoft.com/support/contact/default.asp.

Acknowledgments
===============
Microsoft acknowledges National Bank of Kuwait for bringing this issue to
our attention.

Revisions
=========
 - October 22, 1999: Bulletin Created.

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