Why not ask GM about 0-day vulnerabilities. How much is it going to cost them to 'patch' all the systems? (wait, is that a reverse car analogy...that works?)
As for RF FOBs ...Yes, let's grab my laptop, an adapter, and solder a dozen or so wires to the car's computer, hack in, run some matrix code, and voila...car starts! ...Or jam a screwdriver into the ignition and twist like they do in the movies.
Ok, so neither is reality but it's a general idea. The steering lockout is defeated electrically in one case and mechanically in another - big deal.
Honestly a tow truck driver can have your car in ~15 seconds. See yahhhhhhh........