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

ID: Q193233

The information in this article applies to:

Microsoft Windows NT Workstation version 4.0
Microsoft Windows NT Server version 4.0
Microsoft Windows NT Server version 4.0, Terminal Server Edition

SYMPTOMS

System and network performance could degrade and the Rpcss.exe process could consume 100 percent of CPU time. Analyzing the network with a protocol analyzer shows multiple RPC REJECT packets (addressed to UDP port 135) 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 it appears as if one datagram RPC server sent bad data to another datagram RPC server. The second server returns a REJECT packet. The first server replies with another REJECT packet creating a loop that is not broken until a packet is dropped. If this spoofed UDP packet is sent to multiple computers, an infinite loop may be created, consuming processor resources and network bandwidth.

RESOLUTION

Windows NT 4.0

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

Q152734 How To Obtain the Latest Windows NT 4.0 Service Pack

This hotfix has been posted as Snk-fixi.exe and Snk-fixa.exe. 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/Snk-fix/

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, please see the following article in the Microsoft Knowledge Base:

Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

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

ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40TSE/hotfixes-postSP3/Snk-fix/

STATUS

Microsoft has confirmed this problem could result in some degree of security 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:

http://www.microsoft.com/security/bulletins/ms98-014.asp

Additional query words: denial of service attack snork tse wts

Keywords : NT4SP4Fix kbbug4.00 kbfix4.00.sp4
Version : WinNT:4.0
Platform : winnt
Issue type : kbbug