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Malformed Request to RPC Endpoint Mapper Can Cause RPC Service to Fail

This article has been archived. It is offered "as is" and will no longer be updated.
The RPC (Remote Procedure Call) endpoint mapper allows RPC clients to determine the port number currently assigned to a particular RPC service. Because the endpoint mapper runs within the RPC service itself, if this vulnerability is exploited, the RPC service may fail and any RPC-based services that the server offers and some COM functions may be lost. To restore service, you have to restart the system. Standard security recommendations ask for port 135 (the port on which the RPC endmapper operates) to be blocked at the firewall. If port 135 is blocked, the chief threat posed by this vulnerability is from internal attacks.
This vulnerability results because the Windows NT 4.0 Remote Procedure Call (RPC) service fails if the endpoint mapper is sent a request that contains a particular type of malformed data.
A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that this article describes. Apply it only to systems that you determine are at risk of attack. Evaluate the computer's physical accessibility, network and Internet connectivity, and other factors to determine the degree of risk to the computer. See the associated Microsoft Security Bulletin to help determine the degree of risk. This hotfix may receive additional testing. If the computer is sufficiently at risk, we recommend that you apply this hotfix now.

To resolve this problem immediately, download the hotfix by following the instructions later in this article or contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site: Note In special cases, charges that are ordinarily incurred for support calls may be canceled, if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question. The following file is available for download from the Microsoft Download Center:
DownloadDownload Q305399i.exe now

Note A patch for Windows NT Server 4.0, Terminal Server Edition is forthcoming.
Release Date: September 10, 2001

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:
119591 How to Obtain Microsoft Support Files from Online Services
Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.

The English version of this fix has the following file attributes or later:
   Date         Time   Version        Size     File name    ------------------------------------------------------   01-Nov-2001  17:59  4.0.1381.7102  343,824  Rpcrt4.dll
NOTE: Due to file dependencies, this hotfix requires Microsoft Windows NT 4.0 Service Pack 6a (SP6a).
Microsoft has confirmed that this problem may cause a degree of security vulnerability in Windows NT 4.0.
More information
For more information about this vulnerability, see the following Microsoft Web site:
security_patch DoS denial of service

Article ID: 305399 - Last Review: 01/11/2015 04:22:10 - Revision: 6.0

Microsoft Windows NT Server 4.0, Terminal Server Edition Service Pack 6, Microsoft Windows NT Server 4.0 Standard Edition, Microsoft Windows NT Server 4.0 Enterprise Edition, Microsoft Windows NT Workstation 4.0 Developer Edition

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