Windows NT Slows Down Because of Land Attack

• 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

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)

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

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