NetSim could be an option to explore for simulating VANET attacks. See the section on attacks in VANETs in https://tetcos.com/machine-learning-netsim.html - it explains using an ML based classifier to detect sybil attacks in VANETs.

You could also run NetSim in conjunction with SUMO. In that case SUMO would handle the road traffic simulation while NetSim would manage the wireless communication network simulation.