[pseudo0]

Relay, not replay attack. For vehicles that unlock and push to start based on the proximity of the key, basically all you need to do is use a pair of software defined radios to trick the car into thinking that the key is there. Hence a relay attack, where one attacker is located near the key and the other is located near the vehicle, and the two attackers pass the components of the challenge/response to the vehicle via the channel between the two attackers.

[rubatuga]

Don't they use time of flight?

[katbyte]

but that of course would cost more money to implement correctly with no further flaws, and many companies are opting for other solutions: https://www.carwow.co.uk/blog/keyless-car-theft-prevention

many many cars are vulnerable to it and will be for a long time.

[pseudo0]

Newer fobs, sure. But as this article demonstrates, it is very expensive and inconvenient to backport security improvements to millions of vehicles.

[rtpg]

Ah, that makes sense. Thanks for the detailed explanation