Microsoft Security Bulletin (MS00-036)
Patch Available for "ResetBrowser Frame" and "HostAnnouncement
Originally posted: May 25, 2000
Microsoft has released a patch that eliminates two security
vulnerabilities, one affecting Microsoft(r) Windows NT(r) 4.0 and
Windows(r) 2000, and the other affecting Windows NT 4.0 only. Under
certain conditions, the vulnerability could allow a malicious user to
make it difficult or impossible for other users to locate services and
computers on a network; in the worst case, it could allow him to
provide incorrect information about the same services and computers.
Frequently asked questions regarding this vulnerability and the
patch can be found at
Windows NT 4.0 and Windows 2000 implement the CIFS Computer Browser
protocol. Two vulnerabilities exist because of the inability of
administrators to limit whether Master Browsers respond to certain
frames. The two vulnerabilities are:
- The "ResetBrowser Frame" vulnerability, which affects both
Windows NT 4.0 and Windows 2000. Like most implementations,
the Windows implementation provides the ability for a Master
Browser to shut down other browsers via the ResetBrowser
frame. However, there is no capability to configure a browser
to ignore ResetBrowser frames. This could allow a malicious
user to shut down browsers on his subnet as a denial of
service attack against the browser service, or, in the worst
case, to shut down all browsers and declare his machine the
new Master Browser.
- The "HostAnnouncement Flooding" vulnerability, which does
not affect Windows 2000. Because there is no means of
limiting the size of the browse table in Windows NT 4.0,
a malicious user could send a huge number of bogus
HostAnnouncement frames to a Master Browser. The resulting
replication traffic could consume most or all of the network
bandwidth and cause other problems in processing the table
If a firewall were in place and blocking port 138 UDP, neither
vulnerability could be exploited by an external user. Even an internal
user could only attack browsers on the same subnet as his machine.
Normal administrative tools would allow the administrator to determine
who had mounted the attack.
Affected Software Versions
- Microsoft Windows NT 4.0 Workstation
- Microsoft Windows NT 4.0 Server
- Microsoft Windows NT 4.0 Server, Enterprise Edition
- Microsoft Windows 2000 Professional
- Microsoft Windows 2000 Server
- Microsoft Windows 2000 Advanced Server
NOTE: Windows 95, Windows 98, and Windows NT 4.0 Server, Terminal
Server Edition, also provide an implementation of the Computer Browser
protocol. However, they are not listed as affected products because
the scenario in which these vulnerabilities could be exploited - large
networks that rely on computer browsing - are exactly the ones most
unlikely to use Windows 95, Windows 98 or Windows NT 4.0 Terminal
Servers as master browsers.
- Windows NT 4.0 Workstation, Server, and Server, Enterprise Edition:
- Windows 2000:
Note Additional security patches are available at the Microsoft
Please see the following references for more information related to
- Frequently Asked Questions: Microsoft Security Bulletin MS00-036,
- Microsoft Knowledge Base article Q262694 discusses this issue and
will be available soon.
- Microsoft Knowledge Base article Q263307 discusses this issue and
will be available soon.
- CIFS/E Browser Protocol,
- Microsoft TechNet Security web site,
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
Microsoft thanks the following people for working with us to protect
- COVERT Labs at PGP Security, Inc. (http://www.nai.com/), for
reporting the "ResetBrowser Frame" vulnerability to us.
- David Litchfield of Cerberus Information Security, Ltd,
(http://www.cerberus-infosec.co.uk/) for reporting the
"HostAnnouncement Flooding" vulnerability to us.
- May 25, 2000: Bulletin Created.
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Last Updated May 25,2000