DOCUMENT:Q192292 09-AUG-2001 [winnt] TITLE :Unpredictable TCP Sequence Numbers in SP4 PRODUCT :Microsoft Windows NT PROD/VER:winnt:4.0,4.0a OPER/SYS: KEYWORDS:kbFEA kbWinNT400sp4fea ====================================================================== ------------------------------------------------------------------------------- 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 ------------------------------------------------------------------------------- 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 ====================================================================== 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 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.