Methods, apparatus, systems, and articles of manufacture are disclosed to detect attacks in V2X networks. An example apparatus includes a challenge handler to (a) transmit a first challenge packet to a first vehicle to request a transmission of a first response, (b) instruct a second challenge packet to be transmitted to a second vehicle to request a transmission of a second response, (c) increment a first counter when the first response is not obtained, (d) increment a second counter when the second response is not obtained, and (e) after repeating (a)-(d), determine that the first and second vehicles are phantom vehicles associated with an attacker with a half-duplex radio when at least one of the first or second counters satisfy a threshold, and a network interface to instruct a third vehicle associated with the V2X network to ignore future messages from the phantom vehicles based on the determination.