The more that a computer controls a system the less secure something is...keep that in mind as a general rule of thumb.
While I do have some experience in the field, I don't have a Toyota or Lexus affected by this type of attack nor the wiring and logic diagrams for an affected vehicle, so can only speak to this from afar...how applicable the following is up to you to decide, though it probably hits pretty close to the mark.
The problem is
CANBUS is not encrypted and is being hijacked. Though the lights are off, the communications lines are still alive and active. Depending on how the bus is segmented it can be "relatively" easy to inject "Front Driver Side Door Inside Unlock." It
should not be easy, however the problem being the Convenience Bus wiring (used for remote entry) may be used by the Tire Pressure Control Module (low bandwidth), Frontal Control Module (lights, low bandwidth), Access Control Module (low bandwidth), etc... Depending, these are different buses multiplexing for bandwidth (sharing time on the same data wires), so while it's not "easy" to get the signalling correct it appears someone figured out how to jump on the wiring, multiplex onto the ACM bus, and send an unlock packet.
I was totally surprised on the next step, pairing a smart key with the Remote Keyless Entry is not at all hard--it takes 15 seconds if automated.* Once that's done it's easy to use the rogue smart key to get the handshake certified. I know a different Japanese manufacturer is pretty rigorous about it, getting a new fob activated requires dealer intervention and authorization from H.Q. in Japan, and the dealer tends to soak the customer for $500 plus $125 for the fob, unlike Toyota where the owner can pair a new fob themselves (a huge win for Toyota/Lexus owners).** However, Toyota certainly could have improved the process by adding layered authentication.
Once the fob-vehicle handshake is certified, injecting "Start/Stop Button Press" isn't hard, it's just a convenience for the thief at this point.***
*RKE Module surface attacks are well known, the CANBUS attack while more complicated is simply a more expedient method.
**This is consistent with Toyota mentality of making easy-to-use/easy-to-maintain/easy-to-repair products.
***Some security details not necessary to the core understanding have been omitted.
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So, what to do....
If you've been around a while the first thing that comes to mind is probably a switch interrupting the starter relay coil wire. A reed switch can be hidden in the dash and activated with a magnet; it can be bypassed but a thief would need a bit of time to figure it out, plus a few more tools. Chances are another theft attempt at a later date will be contemplated, if there's a good chance of success the vehicle might be gone within a week.
An ultimate (and poor) solution is to put a remote on the ECU power, something like:
Remote Control Battery Disconnect Switch Kill Switch for Car with 2 Keys Anti-Theft DC12V 200A Electromagnetic Solenoid Valve Terminal
I am NOT suggesting this--the ECU is not meant to be power cycled and doing so would cause a constant loss of stored settings (like engine tuning). Also of importance: the secondary remote system (such as in the Amazon link) reliability and security strength is unknown.
Getting steel shield plates bent and installed, plus disabling the remote (via ECU "disable" option, a setting stored in the ECU) could possibly be the best solution at the moment, as it will avoid the damage to the wiring and forestall or prevent theft.
Otherwise, a
physical bus in the CANBUS system contains a CAN_High and CAN_Low wire.
- CAN: Controller Area Network
- bus: A communication standard that allows microcontrollers and devices to communicate with each other.
- Serial communication: The process of sending data one bit at a time, sequentially, over a communication channel or computer bus.
- CAN bus: A serial communication transport designed for robust performance within harsh environments (primarily automotive and industrial applications).
- Attack surface: The number of all possible points, or attack vectors, where an unauthorized user can access a system. The smaller the attack surface, the easier it is to protect.
I'm going to guess on a Lexus there are two bus lines for the front, a Frontal Control Module-Left & Frontal Control Module-Right (these systems typically have the lights and possibly other sensors on them). If so, putting a
Quad-Pole Single-Throw electronic switch on the bus lines for the FCM-L and FCM-R would disconnect them from the ECU, so all systems using the FCML and RCMR buses could potentially communicate with each other (if powered), but not the ECU.**** Since the door lock relay is usually on a different physical bus than the headlights (different wires), injecting Convenience commands should go unanswered.*^ I'd guess the Remote Keyless Entry receiver is under the dash or mounted to an A-pillar on a different physical bus, so the keyfob should still allow remote entry.
**** Do not assume a device is unpowered during an attack as power can be injected.
*^ The headlights and doors should be on different physical wires, so tapping into one system shouldn't allow communication with the other except through the ECU, which in this case would have been disconnected via tying 4 pins high on the electronic switch which opens the FCM bus lines, disconnecting the lights from the ECU.
Concerning the keyfob, there's a remote attack surface that's not uncommon, the following video explains it well. I would guess there's an ECU setting to disable this
(until the ECU setting is reset to the default value).