source: https://www.securityfocus.com/bid/8730/info

It has been reported that Half-Life clients may be prone to a format string vulnerability. The problem occurs when an invalid command is issued to the server, and an error response is returned and displayed by the client. If a format specifier were included within the invalid command, when displaying the error the format specifier would be interperted literally. This could potentially be exploited by a remote attacker to execute arbitrary code with the privileges of the Half-Life client.

https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/23198.zip