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Original issue date: July 31, 2003
Last revised: July 31, 2003 21:25 UTC-0400
Source: CERT/CC

A complete revision history is at the end of this file.

Systems Affected

  • Microsoft Windows NT 4.0
  • Microsoft Windows NT 4.0 Terminal Services Edition
  • Microsoft Windows 2000
  • Microsoft Windows XP
  • Microsoft Windows Server 2003


The CERT/CC is receiving reports of widespread scanning and exploitation of two recently discovered vulnerabilities in Microsoft Remote Procedure Call (RPC) Interface.

I. Description

Reports to the CERT/CC indicate that intruders are actively scanning for and exploiting a vulnerability in Microsoft's DCOM RPC interface as described in VU#568148 and CA-2003-16. Multiple exploits for this vulnerability have been publicly released, and there is active development of improved and automated exploit tools for this vulnerability. Known exploits target TCP port 135 and create a privileged backdoor command shell on successfully compromised hosts. Some versions of the exploit use TCP port 4444 for the backdoor, and other versions use a TCP port number specified by the intruder at run-time. We have also received reports of scanning activity for common backdoor ports such as 4444/TCP. In some cases, due to the RPC service terminating, a compromised system may reboot after the backdoor is accessed by an intruder.

There appears to be a separate denial-of-service vulnerability in Microsoft's RPC interface that is also being targeted. Based on current information, we believe this vulnerability is separate and independent from the RPC vulnerability addressed in MS03-026. The CERT/CC is tracking this additional vulnerability as VU#326746 and is continuing to work to understand the issue and mitigation strategies. Exploit code for this vulnerability has been publicly released and also targets TCP port 135.

In both of the attacks described above, a TCP session to port 135 is used to execute the attack. However, access to TCP ports 139 and 445 may also provide attack vectors and should be considered when applying mitigation strategies.

II. Impact

A remote attacker could exploit these vulnerabilities to execute arbitrary code with Local System privileges or to cause a denial of service condition.

III. Solutions

Apply patches

All users are encouraged to apply the patches referred to in Microsoft Security Bulletin MS03-026 as soon as possible in order to mitigate the vulnerability described in VU#568148. These patches are also available via Microsoft's Windows Update service.

Systems running Windows 2000 may still be vulnerable to at least a denial of service attack via VU#326746 if their DCOM RPC service is available via the network. Therefore, sites are encouraged to use the packet filtering tips below in addition to applying the patches supplied in MS03-026.

Filter network traffic

Sites are encouraged to block network access to the RPC service at network borders. This can minimize the potential of denial-of-service attacks originating from outside the perimeter. The specific services that should be blocked include

  • 135/TCP
  • 135/UDP
  • 139/TCP
  • 139/UDP
  • 445/TCP
  • 445/UDP

If access cannot be blocked for all external hosts, the CERT/CC recommends limiting access to only those hosts that require it for normal operation. As a general rule, the CERT/CC recommends filtering all types of network traffic that are not required for normal operation.

Because current exploits for VU#568148 create a backdoor, which is in some cases 4444/TCP, blocking inbound TCP sessions to ports on which no legitimate services are provided may limit intruder access to compromised hosts.

Recovering from a system compromise

If you believe a system under your administrative control has been compromised, please follow the steps outlined in

Steps for Recovering from a UNIX or NT System Compromise


The CERT/CC is tracking activity related to exploitation of the first vulnerability (VU#568148) as CERT#27479 and the second vulnerability (VU#326746) as CERT#24523. Relevant artifacts or activity can be sent to with the appropriate CERT# in the subject line.

Appendix A. Vendor Information

This appendix contains information provided by vendors. When vendors report new information, this section is updated and the changes are noted in the revision history. If a vendor is not listed below, we have not received their comments.


Please see Microsoft Security Bulletin MS03-026.

Appendix B. References

Authors: Chad Dougherty and Kevin Houle

Copyright 2003 Carnegie Mellon University.

Revision History

July 31, 2003: Initial release July 31, 2003: Fixed HREF in References section

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