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
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