CERT-SEI

Buffer Overflow in Windows Workstation Service

Original release date: November 11, 2003
Last revised: Nov. 20, 2003
Source: CERT/CC

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


Systems Affected

  • Microsoft Windows 2000 Service Pack 2, Service Pack 3, Service Pack 4
  • Microsoft Windows XP
  • Microsoft Windows XP Service Pack 1
  • Microsoft Windows XP 64-Bit Edition

Overview

A buffer overflow vulnerability exists in Microsoft's Windows Workstation Service (WKSSVC.DLL).

A remote attacker could exploit this vulnerability to execute arbitrary code or cause a denial of service.


I. Description

Microsoft's Security Bulletin MS03-049 discusses a buffer overflow in Microsoft's Workstation Service that can be exploited via a specially crafted network message.

According to the eEye Digital Security Advisory AD20031111, the vulnerability is caused by a flaw in the network management functions of the DCE/RPC service and a logging function implemented in Workstation Service (WKSSVC.DLL). Various RPC functions will permit the passing of long strings to the vsprintf() routine that is used to create log entries. The vsprintf() routine contains no bounds checking for parameters thus creating a buffer overflow situation.

Two exploits and a proof-of-concept exploit have been reported for this vulnerability.

The CERT/CC is tracking this issue as VU#567620.  This reference number corresponds to CVE candidate CAN-2003-0812.

II. Impact

A remote attacker could exploit this vulnerability to execute arbitrary code with system-level privileges or to cause a denial of service. The exploit vector and impact for this vulnerability are conducive to automated attacks such as worms.

III. Solution

Apply a patch from your vendor

Apply the appropriate patch as specified in Microsoft Security Bulletin MS03-049.

 

    Appendix A contains additional information     provided by vendors for this advisory.  As vendors report new     information to the CERT/CC, we will update this section and note     the changes in our revision history.  If a particular vendor is     not listed below or in the individual vulnerability     notes, we have not received their comments.  Please contact     your vendor directly.  

Restrict access

You may wish to block access from outside your network perimeter, specifically by blocking access to TCP & UDP ports 138, 139, and 445. 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.

The CERT/CC has confirmed that one exploit connects to TCP port 445 on the victim machine to exploit this vulnerability. Once exploitation is successful, it then listens on TCP port 4444. You may wish to monitor for this and other open ports as an indication of exploitation.

Disable the Workstation Service

Depending on site requirements, you may wish to disable the Workstation Service as described in MS03-049.  Disabling the Workstation Service will help protect against this vulnerability, but may also cause undesirable side effects. According to the Microsoft's Security Bulletin, the impacts of disabling the Workstation Service are as follows:

"If the Workstation service is disabled, the system cannot connect to any shared file resources or shared print resources on a network. Only use this workaround on stand-alone systems (such as many home systems) that do not connect to a network. If the Workstation service is disabled, any services that explicitly depend on the Workstation service do not start, and an error message is logged in the system event log. The following services depend on the Workstation service:
       
  • Alerter    
  • Browser    
  • Messenger    
  • Net Logon    
  • RPC Locator

These services are required to access resources on a network and to perform domain authentication. Internet connectivity and browsing for stand-alone systems, such as users on dial-up connections, on DSL connections, or on cable modem connections, should not be affected if these services are disabled.

Note: The Microsoft Baseline Security Analyzer will not function if the Workstation service is disabled. It is possible that other applications may also require the Workstation service. If an application requires the Workstation service, simply re-enable the service. This can be performed by changing the Startup Type for the Workstation service back to Automatic and restarting the system."

Appendix A. - Vendor Information

 

    This appendix contains information provided by vendors for this     advisory.  As vendors report new information to the CERT/CC, we     will update this section and note the changes in our revision     history.  If a particular vendor is not listed below or in the     individual vulnerability     notes, we have not received their comments.  

Microsoft Corporation

Microsoft has released MS03-049.


This vulnerability was discoved by eEye Digital Security and reported in Microsoft Security Bulletin MS03-049.

Author: Jason A Rafail.

Copyright 2003 Carnegie Mellon University.

Revision History

Nov 11, 2003:  Initial release
Nov 20, 2003:  Added information regarding exploits