Black Hat USA 2015: The full story of how that Jeep was hacked

Then, if you want to be sure that the firmware isn't hacked, simply remove the SD card, put it in a computer, and verify the contents. If paranoid, overwrite the SD card with the official firmware. If extremely paranoid, throw away the SD card, buy a new one, and write the official firmware to it.

Remote control over your breaks/steering is a pretty scary scenario. Someone having your physical keys mostly means they can steal your car.

Any form of engineered design is unlikely to go backwards in terms of the functionality and flexibility that things like bus communications bring, but awareness of these new attack vectors needs to be included in the base design.

This is the path that industrial control systems are taking in light of attacks such as Stuxnet, I expect that the automotive guys (who are usually ahead of the game in terms of systems engineering) will follow suit.

Edit: The problem I have with people proposing air gaps and read-only circuitry, is that they just don't work in real applications. If there is a business case against it, such as the service these jeeps were offering, then air gaps and hardwired circuitry solutions will be overridden by that business case. Further than that, as can be seen with things like the Lenovo hardware fiasco, manufacturers cannot be trusted to abide by the rules (such as: air gaps are now mandatory), when there is a benefit for them to act otherwise. As Chrysler now has the ability to remote into their cars, they are very unlikely to remove this ability 'merely' due to safety concerns.

It's far safer on the whole to offer secure methods of achieving the existing or proposed functionality, than to try and walk backwards and make things harder and more costly to implement, for lesser functionality.

The thing is, nobody lets their computer act based on arbitrary packets coming in from the internet. We at LEAST make them take place in the context of a TCP session (layer 5). More likely you'd require node authentication (a function of the application layer, layer 7).

I have real doubts that manufacturers can/will implement airgaps and read-only circuitry properly. Jeep tried, and now they're doing a recall. Auto companies are only starting to realize that they are actually in the business of computer security now, and it will be years before there's been enough of these recalls for them to come to terms with the magnitude of this task. The fact that they are still operating on the walled-garden concept - inside of which all messages are taken on face value - is ample evidence of this.

Real airgaps imply a severe degradation of functionality from what both consumers and auto companies have come to expect. The days of your entertainment unit being able to control anything in your car will be gone, as will things like over-the-air firmware updates, remote door unlocks, etc. This is just not going to happen in a feature-driven world. And all it takes is for someone to leave one firmware-flash bit unset and the entire thing is worthless. Expecting that airgaps and read-only circuitry will be implemented, and implemented perfectly, every time, is wildly unrealistic, and with that security model the failure case is brutal. Once they're into the garden, they're in.

Burying your head in the sand or bawling about the cost of the fix is pointless. Cars are now connected to the internet and broadcast wifi networks, they can no longer blindly trust messages on their internal networks. That's the thing auto companies have to fundamentally come to grips with, regarding them now being in the business of computer security. If you want cars to be on the internet, validating signing for messages, firmware updates, etc is not optional, regardless of what you would prefer. We need UEFI for car hardware, and we need messages authenticated on a session level. The brakes need to be able to realize that there's no valid reason for the head unit to be sending them commands.