Q243835: MS99-046: How to Prevent Predictable TCP/IP Initial Sequence Num
Article: Q243835
Product(s): Microsoft Windows NT
Version(s): 4.0,4.5
Operating System(s):
Keyword(s): kbnetwork kbSecurity kbWinNT400PreSP7Fix kbgraphxlinkcritical KbSECVulnerability
Last Modified: 09-MAY-2002
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The information in this article applies to:
- Microsoft Windows NT Server version 4.0, Terminal Server Edition
- Microsoft Windows NT Workstation version 4.0
- Microsoft Windows NT Server version 4.0
- Microsoft Windows NT Server, Enterprise Edition version 4.0
- Microsoft BackOffice Server versions 4.0, 4.5
- Microsoft BackOffice Small Business Server versions 4.0, 4.5
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SYMPTOMS
========
When you use Microsoft TCP/IP on a computer running Windows NT 4.0, you may be
able to predict a session's initial sequence numbers (ISN). Someone can use this
information to attack a computer by posing as a trusted user.
RESOLUTION
==========
Windows NT Server or Workstation 4.0
------------------------------------
To resolve this problem, obtain the individual package referenced below or obtain
the Windows NT 4.0 Security Rollup Package. For additional information on the
SRP, click the article number below to view the article in the Microsoft
Knowledge Base:
Q299444 Post-Windows NT 4.0 Service Pack 6a Security Rollup Package (SRP)
NOTE: This fix was reposted on November 9, 1999 to resolve the following error
message encountered while applying the hotfix:
Hotfix setup has detected that the service pack version of the system
installed is newer than the update you are applying to it.
The following files are available for download from the Microsoft Download
Center. Click the file names below to download the appropriate file:
If you are running Windows NT 4.0 Service Pack 6a:
x86:
Microsoft Download Center: DownloadDownload Q243835i.exe now
(http://download.microsoft.com/download/winntsrv40/Patch/TCP-SP6/NT4/EN-US/Q243835i.exe)
Alpha:
Microsoft Download Center: DownloadDownload Q243835a.exe now
(http://download.microsoft.com/download/winntsrv40/Patch/TCP-SP6/NT4/EN-US/Q243835a.exe)
If you are running Windows NT 4.0 Service Pack 5:
x86:
Microsoft Download Center: DownloadDownload Q243835sp5i.exe now
(http://download.microsoft.com/download/winntsrv40/Patch/TCP-SP5/NT4/EN-US/Q243835sp5i.exe)
Alpha:
Microsoft Download Center: DownloadDownload Q243835sp5a.exe now
(http://download.microsoft.com/download/winntsrv40/Patch/TCP-SP5/NT4/EN-US/Q243835sp5a.exe)
For additional information about how to download Microsoft Support files, click
the article number below to view the article in the Microsoft Knowledge Base:
Q119591 How to Obtain Microsoft Support Files from Online Services
Microsoft used the most current virus detection software available on the date of
posting to scan this file for viruses. After it is posted, the file is housed on
secure servers that prevent any unauthorized changes to the file.
Windows NT Server 4.0, Terminal Server Edition
----------------------------------------------
To resolve this problem, either obtain the hotfix referenced in this section or
the Windows NT Server 4.0, Terminal Server Edition, Security Rollup Package
(SRP). For additional information about the SRP, click the article number below
to view the article in the Microsoft Knowledge Base:
Q317636 Windows NT Server 4.0, Terminal Server Edition, Security Rollup
Package
The following files are available for download from the Microsoft Download
Center:
x86:DownloadDownload Q243835i.exe now
(http://download.microsoft.com/download/winntterminal/Patch/Q243835/NT4ALPHA/EN-US/Q243835i.exe)
Alpha:DownloadDownload Q243835a.exe now
(http://download.microsoft.com/download/winntterminal/Patch/Q243835/NT4ALPHA/EN-US/Q243835a.exe)
For additional information about how to download Microsoft Support files, click
the article number below to view the article in the Microsoft Knowledge Base:
Q119591 How to Obtain Microsoft Support Files from Online Services
Microsoft used the most current virus detection software available on the date of
posting to scan this file for viruses. After it is posted, the file is housed on
secure servers that prevent any unauthorized changes to the file.
STATUS
======
Windows NT 4.0
--------------
Microsoft has confirmed that this problem could result in some degree of security
vulnerability in Windows NT 4.0.
Windows NT Server 4.0, Terminal Server Edition
----------------------------------------------
Microsoft has confirmed that this problem could result in some degree of security
vulnerability in Windows NT Server 4.0, Terminal Server Edition.
MORE INFORMATION
================
In the TCP/IP protocol suite, data is exchanged in the form of packets. Because
of the way TCP/IP performs routing, the path taken by packets can change
dynamically throughout a session. This means that if Host A and B are
communicating and Host A sends two packets, they could potentially take
different paths to Host B, and could arrive out of order. Host B must therefore
have a way to re-assemble the packets (containing the data in octets) in correct
order.
TCP/IP provides a way to do this using sequence numbers. Starting from an initial
sequence number (ISN) that each host provides as part of the session setup, each
octet is assigned a sequence number that is one larger than that of its
predecessor. For example, if Host B provides 123 as the initial sequence number
for its session with Host A, Host A's first octet is numbered 123, the second is
numbered 124, the third is numbered 125, etc.
If someone attempts to launch an attack against another computer and the attacker
can predict how a host selects ISNs, it's possible to conduct two types of
attacks, known as IP address spoofing and session hijacking. The more random the
ISNs are, the more difficult it is to carry out these attacks.
For related information on this problem, please visit the following Microsoft Web
site:
http://www.microsoft.com/technet/security/bulletin/MS99-046.asp
For additional security-related information about Microsoft products, please
visit the following Microsoft Web site:
http://www.microsoft.com/technet/security/
Additional query words: security_patch kbtsesrp
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Keywords : kbnetwork kbSecurity kbWinNT400PreSP7Fix kbgraphxlinkcritical KbSECVulnerability
Technology : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400 kbWinNTS400search kbWinNTS400 kbNTTermServ400 kbNTTermServSearch kbAudDeveloper kbBackOfficeSearch kbSBServSearch kbBackOfficeServ400 kbBackOfficeServ450 kbSBServ400 kbSBServ450
Version : :4.0,4.5
Hardware : ALPHA x86
Issue type : kbbug
Solution Type : kbfix
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