Pakistan Computer Emergency Response Team

The Security Standard


Copyright | Disclaimer




Exploitation of Vulnerabilities in Microsoft RPC Interface


CERT Advisory CA-2003-19 Exploitation of Vulnerabilities in Microsoft RPC

Original issue date: July 31, 2003
Last revised: -
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

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

* CERT/CC Vulnerability Note VU#561284 -
* CERT/CC Vulnerability Note VU#326746 -
* Microsoft Security Bulletin MS03-026 -
* Microsoft Knowledge Base article 823980 -

Authors: Chad Dougherty and Kevin Houle

This document is available from:

CERT/CC Contact Information

Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890

CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) /
EDT(GMT-4) Monday through Friday; they are on call for emergencies
during other hours, on U.S. holidays, and on weekends.

Using encryption

We strongly urge you to encrypt sensitive information sent by email.
Our public PGP key is available from

If you prefer to use DES, please call the CERT hotline for more

Getting security information

CERT publications and other security information are available from
our web site

To subscribe to the CERT mailing list for advisories and bulletins,
send email to Please include in the body of your

subscribe cert-advisory

* "CERT" and "CERT Coordination Center" are registered in the U.S.
Patent and Trademark Office.

Any material furnished by Carnegie Mellon University and the Software
Engineering Institute is furnished on an "as is" basis. Carnegie
Mellon University makes no warranties of any kind, either expressed or
implied as to any matter including, but not limited to, warranty of
fitness for a particular purpose or merchantability, exclusivity or
results obtained from use of the material. Carnegie Mellon University
does not make any warranty of any kind with respect to freedom from
patent, trademark, or copyright infringement.

Conditions for use, disclaimers, and sponsorship information

Copyright 2003 Carnegie Mellon University.

Revision History

July 31, 2003: Initial release

Version: PGP 6.5.8


All rights reserved. Copyright© PakCERT 2000-2018