As connected vehicles are envisioned to provide novel intelligent transportation systems, cyberattacks and security schemes are becoming an increasing concern. Several studies have shown that algorithms that make use of location information from other vehicles, such as vehicular platoon controllers, are vulnerable to message falsification attacks. Moreover, the ability for an attacking vehicle to appear as several vehicles through a so-called Sybil attack can significantly increase the severity of the attack. In this paper, we investigate how these attacks can be detected using Vouch location proof scheme (by identifying false location messages) and propose several reaction strategies to mitigate them. We also show through simulation that it is possible to prevent collisions by reacting appropriately to the false beacons in time while not reacting to false positives coming from the detector.