Microsoft Security Bulletin (MS00-047)
Patch Available for "NetBIOS Name Server Protocol Spoofing" Vulnerability Originally Posted: July 27, 2000
Microsoft has released a patch that eliminates a security vulnerability in a protocol implemented in Microsoft(r) Windows(r) systems. It could be used to cause a machine to refuse to respond to requests for service.
Frequently asked questions regarding this vulnerability and the patch can be found at http://www.microsoft.com/technet/security/bulletin/fq00-047.asp
The NetBIOS Name Server (NBNS) protocol, part of the NetBIOS over TCP/IP (NBT) family of protocols, is implemented in Windows systems as the Windows Internet Name Service (WINS). By design, NBNS allows network peers to assist in managing name conflicts. Also by design, it is an unauthenticated protocol and therefore subject to spoofing. A malicious user could misuse the Name Conflict and Name Release mechanisms to cause another machine to conclude that its name was in conflict. Depending on the scenario, the machine would as a result either be unable to register a name on the network, or would relinquish a name it already had registered. The result in either case would be the same - the machine would not respond requests sent to the conflicted name anymore.
If normal security practices have been followed, and port 137 UDP has been blocked at the firewall, external attacks would not be possible. A patch is available that changes the behavior of Windows systems in order to give administrators additional flexibility in managing their networks. The patch allows administrators to configure a machine to only accept a name conflict datagram in direct response to a name registration attempt, and to configure machines to reject all name release datagrams. This will reduce but not eliminate the threat of spoofing. Customers needing additional protection may wish to consider using IPSec in Windows 2000 to authenticate all sessions on ports 137-139.
Note Additional security patches are available at the Microsoft Download Center
Please see the following references for more information related to this issue. - Frequently Asked Questions: Microsoft Security Bulletin MS00-047, http://www.microsoft.com/technet/security/bulletin/fq00-047.asp - Microsoft Knowledge Base article Q269239 discusses this issue and will be available soon. - Protocol Standard for a NetBIOS Service on a TCP/UDP Transport: Concepts and Methods, RFC 1001. - Protocol Standard for a NetBIOS Service on a TCP/UDP Transport: Detailed Specification, RFC 1002. - Microsoft TechNet Security web site, http://www.microsoft.com/technet/security/default.asp
This is a fully supported patch. Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/support/contact/default.asp.
Microsoft thanks the following customers for working with us to protect customers:
COVERT Labs at PGP Security, Inc., for reporting the unsolicited NetBIOS Name Conflict datagram issue to us. Sir Dystic of Cult of the Dead Cow for reporting the Name Release issue to us.
July 27, 2000: Bulletin Created.
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