[jimbomins]

That's not strictly fair. The problem is that the critical systems were moved to share transport on the main hub with infotainment (safe, I did modelling of the messages for Volvo way back). On that hub is wireless access. Cars have been using CANBUS way longer than that issue entering play and without physical access you wouldn't be able to hack them and with physical access you could easily tamper with brakes or other systems.

[AlotOfReading]

Dealerships routinely violate CANbus isolation with junky "add-ons" full of security holes and wireless interfaces directly attached to important buses. Every single manufacturer that cares at all about bus integrity should be doing message signing and that's where CANBus simply doesn't work. The bandwidth is far too low for good schemes (leading to custom implementations) and there are no decent standards for hardware vendors to implement, which means more of the already-limited CPU budget has to be allocated to it.