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CA-2003-28 Buffer Overflow in Windows Workstation Service

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CERT Advisory CA-2003-28 Buffer Overflow in Windows Workstation Service

Original release date: November 11, 2003
Last revised: --
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
<http://www.microsoft.com/technet/security/bulletin/MS03-049.asp>
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.

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.

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.
______________________________________________________________________

This document is available from:
http://www.cert.org/advisories/CA-2003-28.html
______________________________________________________________________

CERT/CC Contact Information

Email: cert@cert.org
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
U.S.A.

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______________________________________________________________________

NO WARRANTY
Any material furnished by Carnegie Mellon University and the Software
Engineering Institute is furnished on an "as is" basis. Carnegie
Mellon University makes no warranties of any kind, either expressed or
implied as to any matter including, but not limited to, warranty of
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______________________________________________________________________

Conditions for use, disclaimers, and sponsorship information

Copyright 2003 Carnegie Mellon University.

Revision History
Nov 11, 2003: Initial release

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