Comment by Too

Single network? All manufactures i've worked with in recent times have tons of internal networks and buses. Some are more isolated than others, eg connected infotainment and OBD often being behind some kind of secure gateway to not have direct access to engine network. If anyone is aware of manufacturers that don't do this please shout out.

But yeah, otherwise the data buses are kindof assumed to be internal and only contain trusted input, only recently some cars are now also starting to have cryptographically signed packets. It's really not such a big deal until you mix connected ecus with secure ecus or install cheap third party stuff yourself on same network, if someone could physically access the data bus there are other more dangerous things they could do anyway.