and to be fair, the systems (apparently) are intentionally built for remote access.
they could be hacked over the air
they could be hacked through an onboard backdoor
they could be hacked by a compromised military system on the ground
we, here, can't really know the exact mechanism but it's well within known technical capabilities to see any of the three as the attack vector.
shit, the cia was crashing benzes in what the 90s?