source: https://www.securityfocus.com/bid/36061/info

Source Engine is prone to a format-string vulnerability because it fails to properly sanitize user-supplied input before passing it as the format specifier to a formatted-printing function.

An attacker may exploit this issue to execute arbitrary code in the context of the vulnerable application. Failed exploit attempts will likely result in a denial-of-service condition.

Source Engine 3968 and prior builds are affected.

https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/33172-1.zip
https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/33172-2.zip