source: http://www.securityfocus.com/bid/5076/info

Half-Life is a popular game distributed and maintained by Valve Software. It includes features that allow users to game locally, or in distributed network environments. Valve Software also distributes a dedicated server product.

A denial of service vulnerability has been reported in some versions of the Half-Life server. A remote party may create a large number of new users on a specific server through spoofing the connection conversation. As servers contain a set limit on the maximum number of players, server resources will be exhausted, and legitimate players will not be allowed to join the game. 

https://github.com/offensive-security/exploit-database-bin-sploits/raw/master/bin-sploits/21572.zip