DOCUMENT:Q165005
TITLE   :Windows NT Slows Down Due to Land Attack
PRODUCT :Microsoft Windows NT
PROD/VER:3.51 4.00
OPER/SYS:WINDOWS
KEYWORDS:kbbug kbbug3.51 kbbug4.00 kbenv kbfix3.51 kbfix4.00 kbpatch NTSrvWkst nttcp

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The information in this article applies to:

 - Microsoft Windows NT Workstation versions 3.51 and 4.0
 - Microsoft Windows NT Server versions 3.51 and 4.0
 - Microsoft Windows NT Server Enterprise Edition version 4.0
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SYMPTOMS
========

After receiving spoofed connection request (SYN) packets, Windows NT may
begin to operate slowly. After about one minute, Windows NT returns to
normal operation.

NOTE: This problem may occur with TCP/IP on other operating systems as
well.

CAUSE
=====

This behavior occurs because of "Land Attack." Land Attack sends SYN
packets with the same source and destination IP addresses and the same
source and destination ports to a host computer. This makes it appear as if
the host computer sent the packet to itself. Windows NT operates more
slowly while the host computer tries to respond to itself.

RESOLUTION
==========

Microsoft has updated Tcpip.sys to correct the problem. Instructions for
installing it are available from Microsoft support channels, or directly
from the Internet locations below.

NOTE: This hotfix was originally posted on November 26, 1997. A subsequent
fix was completed on January 9, 1998 to address another nearly identical
attack and this hotfix has replaced the original one. The original hotfix
is included in Windows NT 4.0 Service Pack 3. The most recent hotfix is
not; however, it is available from the following Internet locations:

Windows NT 4.0
--------------

To resolve this problem in Windows NT 4.0, obtain the following fix or wait
for the next Windows NT service pack.

This fix should have the following time stamp:

   01/09/98  08:16a               143,664 Tcpip.sys   (Intel)
   01/09/98  08:13a               263,536 Tcpip.sys   (Alpha)

This hotfix has been posted to the following Internet location:

   ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/
   hotfixes-postSP3/teardrop2-fix/

NOTE: The above link is one path; it has been wrapped for readability.

NOTE: This fix supercedes the Land-fix, the ICMP-fix and the OOB-fix
hotfixes.

Windows NT 3.51
---------------

To resolve this problem in Windows NT 3.51, obtain the following fix or
wait for the next Windows NT service pack.

This fix should have the following time stamp:

   01/14/98  12:04p               123,824 Tcpip.sys   (Intel)
   01/14/98  12:00p               216,848 Tcpip.sys   (Alpha)

STATUS
======

Microsoft has confirmed this to be a problem in Windows NT version 4.0.
A supported fix is now available, but has not been fully regression tested
and should be applied only to systems experiencing this specific problem.
Unless you are severely impacted by this specific problem, Microsoft
recommends that you wait for the next Service Pack that contains this fix.
Contact Microsoft Technical Support for more information.

Microsoft has confirmed this to be a problem in Windows NT version 3.51.
A supported fix is now available, but is not fully regression tested and
should be applied only to systems experiencing this specific problem.
Unless you are severely impacted by this specific problem, Microsoft
recommends that you wait for the next Service Pack that contains this fix.
Contact Microsoft Product Support Services for more information.

MORE INFORMATION
================

For information on the hotfix for Windows 95, please see the following
article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q177539
   TITLE     : Windows 95 Stops Responding Because of Land Attack

Additional query words: 3.51 4.00 port 139

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