Epic Games Unreal Engine 226f through 436 does not validate the challenge key, which allows remote attackers to exhaust the player limit by joining the game multiple times.
https://exchange.xforce.ibmcloud.com/vulnerabilities/11304
http://www.securityfocus.com/bid/6771
http://www.pivx.com/luigi/adv/ueng-adv.txt
http://archives.neohapsis.com/archives/bugtraq/2003-02/0142.html
http://archives.neohapsis.com/archives/bugtraq/2003-02/0063.html