[NT] Flaw in ISAPI Extension for Windows Media Services Could Cause Denial of Service
From: SecuriTeam (support_at_securiteam.com)
To: firstname.lastname@example.org Date: 29 May 2003 23:27:22 +0200
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Flaw in ISAPI Extension for Windows Media Services Could Cause Denial of
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
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.
* Microsoft Windows NT 4.0
* Microsoft Windows 2000
Non Affected Software:
* Microsoft Windows XP
* Microsoft Windows Server 2003
* 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.
Download locations for this patch
* Microsoft Windows NT 4.0:
* Microsoft Windows 2000:
What's the scope of the vulnerability?
This is a denial of service vulnerability. An attacker who successfully
exploited this vulnerability could cause a Windows 2000 or Windows NT 4.0
server to step responding to web page requests.
How can an attacker exploit this vulnerability?
An attacker could seek to exploit this vulnerability by constructing a
specific network request and sending it to the server performing logging.
The attacker would have to know which server on the network or internet
was performing logging in order to cause the server to stop responding to
What could this vulnerability enable an attacker to do?
This vulnerability could enable an attacker to cause a denial of service
on a computer running IIS with streaming media logging enabled.
What causes the vulnerability?
The vulnerability results because of an unchecked buffer used by the
nsiislog.dll file for logging. If a specially crafted request is sent to
the server, the logging file will attempt to write a larger buffer than is
possible, which then in turn causes the IIS service to fail.
What is nsiislog.dll?
Nsiislog.dll is an IIS ISAPI extension that was shipped as part of Windows
2000 Server and Advanced Server to provide logging capabilities for Media
Streaming in Microsoft Media Services.
In what versions of IIS might be affected by the vulnerable version of
The vulnerable version of nsiislog.dll can be installed into IIS 4.0, and
What products do IIS 4.0 and 5.0 ship with?
* Internet Information Server 4.0 ships as part of the Windows NT 4.0
Option Pack (NTOP).
* Internet Information Service 5.0 ships as part of Windows 2000
Datacenter Server, Advanced Server, Server and Professional.
Do IIS 4.0, and 5.0 run by default?
* IIS 4.0 runs by default when the NTOP is installed on a Windows NT 4.0
server. It does not run by default when the NTOP is installed on a Windows
NT 4.0 workstation, unless Peer Web Services were already running when it
* IIS 5.0 runs by default on all Windows 2000 server products. It does
not run by default on Windows 2000 Professional.
What are Microsoft Windows Media Services?
Windows Media Services is a feature of Windows 2000 Server, Advanced
Server, and Datacenter Server and provides streaming audio and video
services over corporate intranets and the Internet. In addition, a
downloadable version can be added to Windows NT 4.0.
Can I install Windows Media Services into Windows 2000 Professional or
Windows NT 4.0 Workstation?
No - Windows Media Services are only available for Microsoft Windows
Server operating systems, such as Windows 2000 Server, Advanced Server and
Datacenter Server, or Windows NT 4.0 Server.
What is Multicast Media Streaming?
Multicast media streaming is a method of delivering media content to
clients across a network. As opposed to unicast, method of media
streaming, multicasting sends a single copy of the data to those clients
who request it. Multiple copies of data are not sent across the network,
nor is data processed by clients who do not want it. For more information
on Multicast Media Streaming, please see the following web site:
How can I determine of someone has set up my computer to perform multicast
streaming media logging?
To determine if your computer has been configured for multicast streaming
media logging, perform the following steps:
* From the Start Menu, click search.
* Click For Files or Folders
* In the search dialog, type in the file name, NSIISLOG.DLL
* Click Search Now.
* If the file NSISSLOG.DLL is present in any directory shared by IIS,
then the server is configured for logging of clients of multicast streams.
What does the Patch do?
The fix eliminates the potential for a denial of service attack by
ensuring that the Nsiislog.dll file correctly responds to requests.
The information has been provided by
<mailto:0_48426_E51E4D7D-DECD-43AE-9A29-36080E8D4C3C_US@Newsletters.Microsoft.com> Microsoft Product Security.
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