Techniques are provided for actively controlling a communications bus to mitigate threats, including cyber-attacks. A methodology implementing the techniques according to an embodiment includes detecting a threat in a message that is being transmitted between nodes on the communications bus. The message comprises one or more message frames and the threat detection is based on analysis of an initial portion of the message frame. The method further includes actively controlling the bus, based on the threat detection, to prevent the remaining portion of the message frame from delivering the threat to one or more of the nodes on the bus. Actively controlling the bus includes isolating nodes from the bus and/or overwriting data in the remaining portion of the message frame to invalidate the message frame or to remove the threat from the message frame.