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Rpcss.exe Consumes 100% CPU Due to RPC Spoofing Attack

This article was previously published under Q193233
SYMPTOMS
System and network performance could degrade and the Rpcss.exe processcould consume 100 percent of CPU time. Analyzing the network with aprotocol analyzer shows multiple RPC REJECT packets (addressed to UDP port135) between two or more systems because of an RPC spoofing attack.
CAUSE
This problem is caused by a malicious attack on the remote procedure call(RPC) components in Windows NT.

A UDP packet with a destination port of 135 can be spoofed so that itappears as if one datagram RPC server sent bad data to another datagram RPCserver. The second server returns a REJECT packet. The first server replieswith another REJECT packet creating a loop that is not broken until apacket is dropped. If this spoofed UDP packet is sent to multiplecomputers, an infinite loop may be created, consuming processor resourcesand network bandwidth.
RESOLUTION

Windows NT 4.0

To resolve this problem, obtain the latest service pack for Windows NTversion 4.0. For more information, please see the following article in theMicrosoft Knowledge Base.

152734How To Obtain the Latest Windows NT 4.0 Service Pack

This hotfix has been posted as Snk-fixi.exe and Snk-fixa.exe. For yourconvenience, the English version of this post-SP3 hotfix has been posted tothe following Internet location. However, Microsoft recommends that youinstall Windows NT 4.0 Service Pack 4 to correct this problem.

Windows NT 4.0, Terminal Server Edition

To resolve this problem, obtain the latest service pack for Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in theMicrosoft Knowledge Base:
152734 How to Obtain the Latest Windows NT 4.0 Service Pack

This hotfix has been posted to the following Internet location asSnk-fixi.exe and Snk-fixa.exe:

STATUS
Microsoft has confirmed this problem could result in some degree ofsecurity vulnerability in Windows NT version 4.0 and Windows NT 4.0,Terminal Server Edition. 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.
MORE INFORMATION
For more information, please see the following Microsoft Security Bulletin:
denial of service attack snork tse wts
Properties

Article ID: 193233 - Last Review: 11/01/2006 07:29:02 - Revision: 4.1

  • Microsoft Windows NT Server 4.0, Terminal Server Edition
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Server 4.0 Standard Edition
  • kbbug kbfix KB193233
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