This is not Android Auto though, which is an entirely different product suite designed to connect a OEM infotainment system to an Android device owned by the vehicle operator. That protocol is proprietary, Google-owned and managed, not part of AOSP, and not available to the integrator of the software in question.

The actually vulnerable system is a custom vehicle head unit that merely happens to be running a software stack based on AOSP. It's not even "Android" in a product marketing sense.

Again, it's like blaming Debian because some loon stuffed it in a wifi NAS or whatever and put a backdoor into their UI. It's insane.