Reverse Engineering Marine Propulsion: Bypassing Proprietary CAN Bus Controls

TLDR: Modern marine propulsion systems rely on proprietary CAN bus protocols to manage engine throttle and steering, creating a massive, undocumented attack surface. By intercepting these signals and using simple DACs to spoof legitimate commands, researchers can achieve full autonomous control over powerboats. This research highlights the critical need for security-conscious design in industrial control systems where safety-critical functions are often hidden behind "black box" obscurity.

Marine engines are no longer just mechanical beasts governed by cables and linkages. They are complex, networked industrial control systems. As manufacturers push for more efficiency and integration, they have moved toward fully digital controls, including electronic throttle bodies and integrated steering. This shift has created a dangerous reality for anyone relying on these systems: the security of your boat is now entirely dependent on the integrity of a proprietary, undocumented CAN bus network.

The Anatomy of the Black Box

Most major outboard manufacturers like Mercury, Yamaha, Honda, and Suzuki have consolidated the market, and they are notoriously protective of their control protocols. When you buy a high-end outboard motor, you are not just buying an engine; you are buying into a closed ecosystem. These systems use proprietary CAN bus messages to communicate between the helm and the engine control unit (ECU).

The research presented at DEF CON 33 demonstrates that these "black box" systems are not secure; they are simply obscure. The primary vulnerability here is the lack of authentication or encryption on the CAN bus. Once you gain physical access to the wiring harness, you can sniff the traffic. Because these systems are designed for reliability rather than security, they often lack basic message integrity checks. If you can inject a valid-looking CAN message, the ECU will execute it without question.

Replicating Proprietary Signals

The most effective way to manipulate these engines is not by trying to reverse-engineer the entire proprietary protocol stack, which is a massive time sink. Instead, the focus should be on the user-space interface—the helm. By intercepting the signals between the throttle handle and the command module, you can identify the specific voltage ranges or CAN IDs that correspond to throttle position and gear selection.

For systems using analog signals, you can use a Digital-to-Analog Converter (DAC) to inject the exact voltage levels the ECU expects. If the system uses CAN, you can use a standard CAN interface to spoof the throttle command. The key is to emulate the human operator. The ECU is looking for a specific rate of change, or "slew rate," in the signal. If you jump from zero to full throttle instantly, the system will likely error out as a safety precaution. By carefully crafting your injected signals to match the expected slew rate, you can take control of the engine without triggering a fault.

Real-World Engagement and Impact

For a penetration tester, encountering these systems in the wild is becoming more common as autonomous maritime vessels and remote-operated boats gain traction. During an engagement, your primary goal is to identify the command bus. Look for the wiring harness connecting the helm controls to the engine. Once you have physical access, use a tool like MAVProxy to monitor the traffic. While MAVProxy is typically used for ArduPilot, the underlying principles of signal translation apply to any CAN-based control system.

The impact of a successful compromise is severe. An attacker could remotely manipulate the throttle or steering, leading to collisions or engine damage. Because these systems are often used in critical infrastructure, the potential for disruption is significant. If you are testing a vessel, focus on the "user space"—the interface where the human operator interacts with the machine. This is where the security controls are weakest and the attack surface is most accessible.

The Defensive Reality

Defending these systems is difficult because the manufacturers prioritize proprietary control over interoperability. However, the industry must move toward OWASP-aligned security practices for industrial IoT. This means implementing message authentication, using encrypted communication channels, and ensuring that safety-critical commands cannot be spoofed by unauthorized devices on the bus.

If you are a developer working on these systems, stop relying on "security through obscurity." A proprietary protocol is not a security feature. If your system can be controlled by a two-dollar DAC, it is not secure. Start by implementing basic message signing and ensuring that your ECU can distinguish between a legitimate command from the helm and a malicious injection from an unauthorized source.

The era of "air-gapped" mechanical systems is over. As we continue to digitize every aspect of our infrastructure, we must demand that security is built into the hardware from the ground up. If you are a researcher, keep digging into these proprietary buses. The manufacturers will not tell you how they work, but the hardware will. Grab a scope, find the CAN lines, and start listening. You will be surprised at how much control you can gain with just a few lines of code and a basic understanding of the underlying signals.