emfi

This post is a summary of some work on an accepted paper for ESCAR EU 2020. This work was demonstration on certain NXP chips & GM ECUs, but the idea of both the attack & understanding how portable results are is applicable across the entire domain.

NOTE TO CAR TUNERS: I won’t perform this for hire on your ECU, please don’t email me asking this. The cost for me to do this type of work under hire would also be many times the HPTuners fee, and without any of of the actual tuning interface (I’m only attacking the bootloader, I never ever built a reflash tool that would be needed, yet alone the mapping work etc).

You can find links to:
🔧 The full technical paper in PDF
🔧 The talk slides in PDF
🔧 YouTube “video log” during work: Part 1, Part 2, Part 3, Part 4

This work was presented as a way to help automotive system designers understand the “real” threat to their systems, something that is hard to do when tuners hide their methods for commercial reasons. While I don’t know if the method I’m presenting is used by the car tuners, I assume some variant of it has been before (I doubt I’m the “true” discoverer). As I mentioned in the paper, I’m also not the first to turn EMFI onto automotive devices in an academic setting (another nice paper ref’d is the Safety != Security work). One contribution of my work is it directly talks about practicality, something critical for threat modelling but often skipped due to how messy this is. You can build the attack into a “portable rig” as shown here in a final demonstration:

This portable rig is designed to show something along the lines of “pro garage” or “tuner garage” capabilities. It doesn’t need a ton of expertise to execute the attack, and opening up ECUs and probing them is widely done as part of regular tuning already (often called a type of “bench flash”). The real research wasn’t done with the Arduino setup, but instead using ChipWhisperer as part of the triggering with Python scripts searching:

The Arduino demonstration shown previously is not usable as-is for tuning. It’s very fiddly and hasn’t been optimized, so I can’t productize what was shown there easily (you can tell I get sick of people looking for tuning solutions…).

The attack is possible on these devices, as they have a hardware bootloader enabled with some pin on the board. This requires you to short that pin to GND to enter the bootloader mode, at which point the device is looking for a password. Using electromagnetic fault injection, you can bypass the password check such that an incorrect password is accepted.

You can use power analysis to discover some of the timing, as done in the paper. Comparing a good password to a bad password shows a clear point in time where the password logic differs:

Interestingly, you can also see the red “incorrect password” trace appears to spin into an infinite loop (or similar), which would be around cycle 100 on the above figure.

As an important caveat: EMFI works against almost any microcontroller. Thus there is no “flaw” in the NXP MCU or GM usage of it, many other devices can be attacked using this same technique. The NXP MCU has long-term support (meaning it sticks around 15+ years), and was designed long before fault injection was on the radar of these devices as a realistic threat.

See the full paper for more details of the work.