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CERT® Advisory CA-2003-28 Buffer Overflow in Windows Workstation ServiceOriginal release date: November 11, 2003Last revised: Nov. 20, 2003 Source: CERT/CC A complete revision history is at the end of this file. Systems Affected
OverviewA 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. DescriptionMicrosoft'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. ImpactA 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. SolutionApply a patch from your vendorApply 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 accessYou 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 ServiceDepending 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: Appendix A. - Vendor InformationThis 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 CorporationMicrosoft has released MS03-049.
This vulnerability was discoved by eEye Digital Security and reported in Microsoft Security Bulletin MS03-049. Author: Jason A Rafail. This document is available from: http://www.cert.org/advisories/CA-2003-28.html CERT/CC Contact Information
Phone: +1 412-268-7090 (24-hour hotline) Fax: +1 412-268-6989 Postal address: 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 encryptionWe 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 information. Getting security informationCERT publications and other security information are available from our web site * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office.
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Copyright 2003 Carnegie Mellon University. Revision History
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