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Comment by bigiain | Hacker News Reader

Didn't that Wired article about the Jeep hack tell us something about how well that sometimes gets implemented?

From memory, there was an "untrusted trusted entertainment system" network segment, and a firewall which allowed one-way traffic out of the "trusted" vehicle management network (so the entertainment system could get car speed and similar), and the firewall could have it's firmware updated. From the untrusted network segment...

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The problem with the entertainment system hack is that the can bus used in vehicles uses a priority system that is designed so that higher priority device can always claim the bus. If I remember correctly the entertainment system hack moved up the priority of the entertainment system on the bus so that it was higher priority than whatever nominally controls the car. A can bus isn't robust against bad actors and should have been air gapped to any external connection.

Priority doubles as ID in most CAN systems, so changing the priority means you're no longer sending the message to the same endpoint. As you say, though, CAN isn't secure against someone with physical access to the bus.

IMO "the problem" isn't the CAN priority system, it's that a remotely programmable device (the CAN gateway) was connected to both the control network and the internet (via the entertainment center). For something so security critical, it should have been kept as dumb as a box of rocks, and certainly never made network-updatable.

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