Fleet vehicles with smart locking systems were compromised after attackers captured unique signals from key...

This scenario aligns with a Replay Attack against RF-based smart key systems, covered in CEH v13 IoT and OT Hacking. Attackers capture radio-frequency signals transmitted by key fobs and replay them to unlock vehicles.

CEH v13 emphasizes that detecting and preventing such attacks requires monitoring wireless RF signals for anomalies such as signal replay, interference, or jamming patterns. RF analysis helps confirm unauthorized signal capture and retransmission.

Firmware updates may mitigate future vulnerabilities, but confirmation requires RF monitoring. Physical surveillance and smartphone malware controls are unrelated to RF replay attacks. Therefore, option D is correct.