CERT-SEI

Buffer Overflow in Windows Locator Service

Original issue date: January 23, 2003
Last revised: January 24, 2003
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

Overview

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 service.

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 domain.

III. Solution

Apply a patch

Microsoft has provided the following information (contained within MS03-001) to assist you in downloading the appropriate patch for your platform(s):

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
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  • A list of services will be displayed. If "Remote Procedure Call (RPC) Locator" appears in the list, then the locator service is running.
       
  •  
To disable the Windows Locator service, Microsoft recommends the following:

  • An administrator can disable the Locator service by setting the RpcLocator service status to "disabled" in the services control panel.
  • 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, specifically by blocking access to ports 139/TCP and 445/TCP. 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


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


Author: Ian A. Finlay.

Copyright 2003 Carnegie Mellon University.

Revision History

January 23, 2003:  Initial release
January 24, 2003: Added information about which port nubmers to block