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Title:      Flaw in ISAPI Extension for Windows Media Services
            Could Cause Denial of Service (817772)
Date:       28 May 2003
Software:   Microsoft(r) Windows NT(r) 4.0, and Windows(r) 2000
Impact:     Allow an attacker to execute code of their choice
Max Risk:   Moderate
Bulletin:   MS03-019

Microsoft encourages customers to review the Security Bulletins at:
http://www.microsoft.com/technet/security/bulletin/MS03-019.asp
http://www.microsoft.com/security/security_bulletins/ms03-019.asp
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Issue:
======
Microsoft Windows Media Services is a feature of Microsoft Windows
2000 Server, Advanced Server, and Datacenter Server and is also
available as a downloadable version for Windows NT 4.0 Server.
Windows Media Services contain support for a method of delivering
media content to clients across a network known as multicast
streaming. In multicast streaming however, the server has no
connection or knowledge of the clients that may be receiving the
stream coming from the server. To facilitate logging of client
information for the server Windows 2000 includes a capability
specifically designed for that purpose. . To help with this
problem, Windows 2000 includes logging capabilities for multicast
and unicast transmissions.

This capability is implemented as an Internet Services Application
Programming Interface (ISAPI) extension - nsiislog.dll. When
Windows Media Services are installed in Windows NT 4.0 Server or
added through add/remove programs to Windows 2000, nsiislog.dll is
installed to the Internet Information Services (IIS) Scripts
directory on the server.

There is a flaw in the way in which nsiislog.dll processes incoming
requests. A vulnerability exists because an attacker could send
specially formed communications to the server that could cause IIS
to stop responding to Internet requests.

Windows Media Services is not installed by default on Windows 2000,
and must be downloaded to install on Windows NT 4.0. An attacker
attempting to exploit this vulnerability would have to be aware
which computers on the network had Windows Media Services installed
on it and send a specific request to that server. The denial of
service would only affect IIS, and other services on the server
would remain unaffected.

Mitigating Factors:
====================
 - Windows Media Services 4.1 is not installed by default on
Windows 2000, and must be downloaded to install on Windows NT 4.0.
 - Windows Media Services are not available for Windows 2000
Professional or Windows NT 4.0 Workstation
 - The attacker would have to know which server on the network
Windows Media Services had been installed on.

Risk Rating:
============
Moderate

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the
   Security Bulletins at

http://www.microsoft.com/technet/security/bulletin/ms03-019.asp
http://www.microsoft.com/security/security_bulletins/ms03-019.asp

   for information on obtaining this patch.

Acknowledgment:
===============
 - Brett Moore (brett@softwarecreations.co.nz)

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