DOCUMENT:Q154460 08-AUG-2001 [winnt] TITLE :Denial of Service Attack Against WinNT Simple TCP/IP Services PRODUCT :Microsoft Windows NT PROD/VER:winnt:4.0 OPER/SYS: KEYWORDS:kbfile kbnetwork kbWinNT400sp4fix ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Windows NT Workstation version 4.0 - Microsoft Windows NT Server version 4.0 - Microsoft Windows NT Server version 4.0, Terminal Server Edition ------------------------------------------------------------------------------- SYMPTOMS ======== As your computer is being attacked there may be a jump in bandwidth utilization on a subnet containing Windows NT computers and performance may suffer. A network analyzer shows a large amount of UDP traffic, typically from port 19 (chargen). CAUSE ===== A malicious attack may be mounted against Windows NT computers with the Simple TCP/IP Services installed. The attack consists of a flood of UDP datagrams sent to the subnet broadcast address with the destination port set to 19 and a spoofed source IP address. The Windows NT computers running Simple TCP/IP services respond to each broadcast, creating a flood of UDP datagrams. RESOLUTION ========== Windows NT TCP/IP, Windows Sockets, and Simple TCP/IP services have been modified to be more attack resistant. Windows Sockets now supports a new socket option, SO_BROADCAST, that can be set to allow the recvfrom() call to pass broadcast datagrams to the application. The default for this option is OFF. Previous implementations passed broadcasts datagrams to any Windows Sockets application that issued a recvfrom() call. Additionally, the chargen service and other Simple TCP/IP services have been modified to drop any datagrams that have the source port equal to the destination port to prevent "looping" attacks. To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, please see the following article in the Microsoft Knowledge Base: Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack For your convenience, the English version of this post-SP3 hotfix has been posted to the following Internet location. However, Microsoft recommends that you install Windows NT 4.0 Service Pack 4 to correct this problem. ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40/ hotfixes-postSP3/simptcp-fix NOTE: An updated version of this hotfix was posted on August 15, 1997. STATUS ====== Microsoft has confirmed this problem could result in some degree of security vulnerability in Windows NT version 4.0. This problem was first corrected in Windows NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4. Additional query words: 4.00 prodnt chargen attack ====================================================================== Keywords : kbfile kbnetwork kbWinNT400sp4fix Technology : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbNTTermServ400 kbNTTermServSearch Version : winnt:4.0 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.