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CA-2003-23 RPCSS Vulnerabilities in Microsoft Windows


CERT Advisory CA-2003-23 RPCSS Vulnerabilities in Microsoft Windows

Original release date: September 10, 2003
Last revised: --
Source: CERT/CC

A complete revision history can be found at the end of this file.

Systems Affected

* Microsoft Windows NT Workstation 4.0
* Microsoft Windows NT Server 4.0
* Microsoft Windows NT Server 4.0, Terminal Server Edition
* Microsoft Windows 2000
* Microsoft Windows XP
* Microsoft Windows Server 2003


Microsoft has published a bulletin describing three vulnerabilities
that affect numerous versions of Microsoft Windows. Two of these
vulnerabilities are remotely exploitable buffer overflows that may
allow an attacker to execute arbitrary code with system privileges.
The third vulnerability may allow a remote attacker to cause a denial
of service.

I. Description

The Microsoft RPCSS Service is responsible for managing Remote
Procedure Call (RPC) messages. There are two buffer overflow
vulnerabilities in the RPCSS service, which is enabled by default on
many versions of Microsoft Windows. These buffer overflows occur in
sections of code that handle DCOM activation messages sent to the
RPCSS service.

The CERT/CC is tracking these vulnerabilities as VU#483492 and
VU#254236, which correspond to CVE candidates CAN-2003-0715 and
CAN-2003-0528, respectively. The buffer overflows discussed in this
advisory are different than those discussed in previous advisories.

Microsoft has also published information regarding a denial-of-service
vulnerability in the RPCSS service. This vulnerability only affects
Microsoft Windows 2000 systems.

The CERT/CC is tracking this vulnerability as VU#326746, which
corresponds to CVE candidate CAN-2003-0605. This vulnerability was
previously discussed in CA-2003-19.

II. Impact

By exploiting either of the buffer overflow vulnerabilities, remote
attackers may be able to execute arbitrary code with Local System

By exploiting the denial-of-service vulnerability, remote attackers
may be able to disrupt the RPCSS service. This may result in general
system instability and require a reboot.

III. Solution

Apply a patch from Microsoft

Microsoft has published Microsoft Security Bulletin MS03-039 to
address this vulnerability. For more information, please see

This bulletin supersedes MS03-026.

Block traffic to and from common Microsoft RPC ports

As an interim measure, users can reduce the chance of successful
exploitation by blocking traffic to and from well-known Microsoft RPC
ports, including
* Port 135 (tcp/udp)
* Port 137 (udp)
* Port 138 (udp)
* Port 139 (tcp)
* Port 445 (tcp/udp)
* Port 593 (tcp)

To prevent compromised hosts from contacting other vulnerable hosts,
the CERT/CC recommends that system administrators filter the ports
listed above for both incoming and outgoing traffic.

Disable COM Internet Services and RPC over HTTP

COM Internet Services (CIS) is an optional component that allows RPC
messages to be tunneled over HTTP ports 80 and 443. As an interim
measure, sites that use CIS may wish to disable it as an alternative
to blocking traffic to and from ports 80 and 443.

Disable DCOM

Disable DCOM as described in MS03-039 and Microsoft Knowledge Base
Article 825750.

This document was written by Jeffrey P. Lanza and is based upon the
information in MS03-039.

This document is available from:

CERT/CC Contact Information

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Fax: +1 412-268-6989
Postal address:
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Carnegie Mellon University
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Revision History
Sep 10, 2003: Initial release

Version: PGP 6.5.8


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