Microsoft Security Bulletin MS99-046
Patch Available to Improve TCP Initial Sequence Number Randomness
Originally Posted: October 22, 1999
Updated: December 23, 1999
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® Windows NT® 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/technet/security/bulletin/fq99-046.mspx.
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
Vulnerability Identifier: CVE-2000-0328
Windows NT 4.0 Workstation, Windows NT 4.0 Server, and Windows NT 4.0 Server, Enterprise Edition:
- Service Pack 4 and 5 (Intel and Alpha versions):
- Service Pack 6 (Intel and Alpha versions):
- Windows NT 4.0 Server, Terminal Server Edition:
Please see the following references for more information related to this issue.
- Microsoft Security Bulletin MS99-046: Frequently Asked Questions, http://www.microsoft.com/technet/security/bulletin/fq99-046.mspx.
- Microsoft Knowledge Base (KB) article 243835, How to Prevent Predictable TCP/IP Initial Sequence Numbers, http://support.microsoft.com/default.aspx?scid=kb;en-us;243835&sd=tech.
(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.
- Protocol Specification, Transmission Control Protocol, http://www.ietf.org/rfc/rfc0793.txt
- Microsoft Security web site, http://www.microsoft.com/technet/security/default.mspx.
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/contactussupport/?ws=support.
Microsoft acknowledges National Bank of Kuwait for bringing this issue to our attention.
- October 22, 1999: Bulletin Created.
- November 12, 1999: Bulletin changed to announce temporary unavailability of patch.
- December 23, 1999: Bulletin changed to announce reavailability of patch.
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