ICMP Redirect Attack Causes Windows NT Server and Workstation to Hang (225344)


The information in this article applies to:

  • Microsoft Windows NT Workstation 4.0
  • Microsoft Windows NT Workstation 4.0 SP4
  • Microsoft Windows NT Server 4.0
  • Microsoft Windows NT Server 4.0 SP4
  • Microsoft Windows NT Server, Enterprise Edition 4.0
This article was previously published under Q225344
IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SYMPTOMS

Your computer running Windows NT may stop responding (hang) or the computer's performance may degrade drastically when connected to an internetwork segment or to the Internet. Other symptoms may include:
  • The Perfmon tool's Processor Utilization object may indicate 100 percent utilization.
  • Issuing a ROUTE PRINT command at a command prompt shows that the route table has changed.
  • If the computer is disconnected from the network segment or the Internet and then restarted, the problem does not occur again until the computer is reconnected to the network segment or Internet.

CAUSE

This problem is caused by the receipt of multiple Internet Control Message Protocol (ICMP) Redirect packets that are used to change routing table entries. Too many ICMP Redirect packets in a short period of time may cause Windows NT to dedicate an inordinate amount of CPU time to update the routing table and cause the computer to stop responding. In many cases, this scenario indicates a denial of service attack through the use of a program to send multiple ICMP Redirect packets against a specific TCP/IP address.

RESOLUTION

To resolve this problem, obtain the latest service pack for Windows NT. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

152734 How to Obtain the Latest Windows NT 4.0 Service Pack


After you have installed Windows NT 4.0 Service Pack 5, you can enable a Windows NT registry entry that allows your computer to disregard ICMP Redirects. To disable ICMP Redirects:

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
  1. Start Registry Editor (Regedt32.exe).
  2. Go to the following key:

    HKEY_LOCAL_MACHINE\System\Currentcontrolset\Services \Tcpip\Parameters

    NOTE: The above registry key is one path; it has been wrapped for readability.
  3. On the Edit menu, click Add Value, type EnableICMPRedirects, click REG_DWORD in the Data Type box, and then click OK.
  4. Type 0, and then click OK. NOTE: Setting this registry entry to a value of 1 enables ICMP Redirects.
  5. Quit Registry Editor, and then restart the computer.

STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Windows NT version 4.0 Service Pack 5.

MORE INFORMATION

For additional information about ICMP Redirect packets, please see the following article in the Microsoft Knowledge Base:

195686 Explanation of ICMP Redirect Behavior

Modification Type:MajorLast Reviewed:5/14/2003
Keywords:kbbug kbfix kbnetwork kbQFE kbWinNT400sp5fix KB225344
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