Letting Birds Scooters Fly Free
upstart writes:
Submitted via IRC for FatPhil
mjg59 | Letting Birds scooters fly free
Bird produce a range of rental scooters that are available in multiple markets. With the exception of the Bird Zero[1], all their scooters share a common control board described in FCC filings. The board contains three primary components - a Nordic NRF52 Bluetooth controller, an STM32 SoC and a Quectel EC21-V modem. The Bluetooth and modem are both attached to the STM32 over serial and have no direct control over the rest of the scooter. The STM32 is tied to the scooter's engine control unit and lights, and also receives input from the throttle (and, on some scooters, the brakes).
The pads labeled TP7-TP11 near the underside of the STM32 and the pads labeled TP1-TP5 near the underside of the NRF52 provide Serial Wire Debug, although confusingly the data and clock pins are the opposite way around between the STM and the NRF. Hooking this up via an STLink and using OpenOCD allows dumping of the firmware from both chips, which is where the fun begins. Running strings over the firmware from the STM32 revealed "Set mode to Free Drive Mode". Challenge accepted.
[...] In summary: Secrets that are stored on hardware that attackers can run arbitrary code on probably aren't secret, not having verified boot on safety critical components isn't ideal, devices should have meaningful cryptographic identity when authenticating against a remote endpoint.
Bird responded quickly to my reports, accepted my 90 day disclosure period and didn't threaten to sue me at any point in the process, so good work Bird.
[...] (Note: These issues were disclosed to Bird, and they tell me that fixes have rolled out. I haven't independently verified)
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