Windows NT Slows Down Because of Land Attack

ID: Q165005

The information in this article applies to:

Microsoft Windows NT Workstation versions 3.51, 4.0
Microsoft Windows NT Server versions 3.51, 4.0
Microsoft Windows NT Server Enterprise Edition version 4.0
Microsoft Windows NT Server version 4.0, Terminal Server Edition

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, 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/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 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.

Microsoft has confirmed this problem could result in some degree of security vulnerability in Windows NT version 3.51. A fully supported fix is now available, but it has not been fully regression tested and should only be applied to systems determined to be at risk of attack. Please evaluate your system's physical accessibility, network and Internet connectivity, and other factors to determine the degree of risk to your system. If your system is sufficiently at risk, Microsoft recommends you apply this fix. Otherwise, wait for the next Windows NT service pack, which will contain this fix. Please contact Microsoft Technical Support 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: port 139

Keywords : kbenv NT4SP4Fix kbbug4.00 nttcp kbfix4.00.sp4 kbbug3.51 kbfix3.51 NTSrvWkst
Version : WinNT:3.51,4.0
Platform : winnt
Issue type : kbbug