Software Engineering Institute

The SQL Server Resolution Service (SSRS) was introduced in Microsoft SQL Server 2000 to provide referral services for multiple server instances running on the same machine. The service listens for requests on UDP port 1434 and returns the address and port number of the SQL server instance that provides access to the requested database.

In addition to providing referrals, the SSRS is capable of replying to "ping" messages from other SQL servers to confirm its presence on a network. When the service receives such a message, it replies to the transmitting host with an identical reply message. In normal operation, the SSRS service is responsible for replying to ping messages sent by an SQL Server and does not initiate them. However, an attacker can create a forged ping message to one instance of the SSRS (Victim A, port 1434) that appears to originate from another instance (Victim B, port 1434), causing Victim A and Victim B to continuously exchange messages. This cycle will continue to consume server and network resources until one of the servers stops sending packets for one of several reasons, including a restart of the SQL Server, a reboot of the server host, or a network failure.

This vulnerability allows remote attackers to initiate a denial-of-service attack between two Microsoft SQL servers.

Apply a patch

This vulnerability was originally addressed by Microsoft in Security Bulletin MS02-039. In January 2003, Microsoft updated MS02-039 to recommend that customers apply the patch from Microsoft Security Bulletin MS02-061, which addresses additional vulnerabilities. For more information, please see

http://www.microsoft.com/technet/security/bulletin/MS02-039.asp
http://www.microsoft.com/technet/security/bulletin/MS02-061.asp

This vulnerability also affects any products that include the Microsoft Desktop Engine (MSDE) 2000. For more information, please see

http://www.microsoft.com/technet/security/MSDEapps.asp

Block port 1434/udp

As a workaround, system administrators can use a firewall to block port 1434/udp at an appropriate network border, thus preventing external attackers from exploiting this vulnerability.