The MAVLink communication protocol does not require cryptographic authentication by default. When MAVLink 2.0 message signing is not enabled, any message -- including SERIALCONTROL, which provides interactive shell access -- can be sent by an unauthenticated party with access to the MAVLink interface. PX4 provides MAVLink 2.0 message signing as the cryptographic authentication mechanism for all MAVLink communication. When signing is enabled, unsigned messages are rejected at the protocol level.