OpenTTD 0.6.0 through 1.2.1 does not properly validate requests to clear a water tile, which allows remote attackers to cause a denial of service (NULL pointer dereference and server crash) via a certain sequence of steps related to "the water/coast aspect of tiles which also have railtracks on one half."
Debian Linux Security Advisory 2524-1 - Two denial of service vulnerabilities have been discovered in the server component of OpenTTD, a free reimplementation of Transport Tycoon Deluxe.