The HandleCrashedAircraft function in aircraft_cmd.cpp in OpenTTD 0.3.6 through 1.3.2 allows remote attackers to cause a denial of service (out-of-bounds read and crash) by crashing an aircraft outside of the map.

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."

OpenTTD 0.3.5 through 1.1.4 allows remote attackers to cause a denial of service (game pause) by connecting to the server and not finishing the (1) authorization phase or (2) map download, aka a "slow read" attack.