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CA-2003-03 Buffer Overflow in Windows Locator Service


CERT Advisory CA-2003-03 Buffer Overflow in Windows Locator Service

Original issue date: January 23, 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 Server Edition
* Microsoft Windows 2000
* Microsoft Windows XP


A buffer overflow vulnerability in the Microsoft Windows Locator
service could allow a remote attacker to execute arbitrary code or
cause the Windows Locator service to fail. This service is enabled and
running by default on Windows 2000 domain controllers and Windows NT
4.0 domain controllers.

I. Description

A buffer overflow in the Windows Locator service may make it possible
for a remote attacker to execute arbitrary code on a vulnerable system
by sending an overly large request to the Windows Locator service.
Microsoft describes the Windows Locator service as "a name service
that maps logical names to network-specific names." From MS03-001:

A client that is going to make a Remote Procedure Call (RPC) can
call the Locator service to resolve a logical name for a network
object to a network-specific name for use in the RPC. For example,
if a print server has the logical name "laserprinter", an RPC
client could call the Locator service to find out the
network-specific name that mapped to "laserprinter". The RPC client
uses the network-specific name when it makes the RPC call to the

Further information about this vulnerability can be found in Microsoft
Security Bulletin MS03-001 and in CERT/CC Vulnerability Note VU#610986,
which correspond to CVE candidate CAN-2003-0003.

II. Impact

A remote attacker may be able to execute arbitrary code on a
vulnerable system, or cause the Windows Locator service to fail. An
attacker who is able to compromise a domain controller might be able
to cause the compromised domain controller to trust the attacker's

III. Solution

Apply a patch

Disable vulnerable service

Until a patch can be applied, you may wish to disable the Windows
Locator service. To determine if the Windows Locator service is
running, Microsoft recommends the following:

* The status of the "Remote Procedure Call (RPC) Locator" service
and how it is started (automatically or manually) can be viewed in
the Control Panel. For Windows 2000 and Windows XP, use Control
Panel | Administrative Tools | Services, and on Windows NT 4.0,
use Control Panel | Services.

* It is also possible to determine the status of the Locator service
from the command line by entering: net start

* A list of services will be displayed. If "Remote Procedure Call
(RPC) Locator" appears in the list, then the locator service is

To disable the Windows Locator service, Microsoft recommends the

* An administrator can disable the Locator service by setting the
RpcLocator service status to "disabled" in the services control

* The service can also be stopped via the command line using the
sc.exe program, which ships with Windows XP and is included as
part of the Windows 2000 Resource Kit. The following command will
stop the service: sc stop RpcLocator

* To disable the service using the command line tool, use the
following: sc config RpcLocator start= disabled

Restrict access to NetBIOS

You may wish to block access to NetBIOS from outside your network
perimeter. This will limit your exposure to attacks. However, blocking
at the network perimeter would still allow attackers within the
perimeter of your network to exploit the vulnerability. It is
important to understand your network's configuration and service
requirements before deciding what changes are appropriate.

As a best practice, the CERT/CC recommends disabling all services that
are not explicitly required. Before deciding to disable the Windows
Locator service, carefully consider your service requirements. Please
also note that Microsoft is actively deploying the patches for this
vulnerability via Windows Update.

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.

Microsoft Corporation

Please see Microsoft Security Bulletin MS03-001.

Appendix B. References

* Microsoft Security Bulletin MS03-001 -

* CERT/CC Vulnerability Note VU#10986 -

This vulnerability was discovered by David Litchfield of Next
Generation Security Software Ltd and was first described in MS03-001.

Author: Ian A. Finlay.

This document is available from:

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Revision History

January 23, 2003: Initial release

Version: PGP 6.5.8


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