This work presents mitigation strategies against potential cyberattacks on distributed energy resources (DERs), and analyzes the effectiveness of the strategies by simulating the cyberattacks and the mitigation strategies implemented. Cyberat-tacks including solar inverter control manipulation, malicious distributed energy resource management system (DERMS) firmware update, solar forecast data manipulation, and electic vehicle (EV) charging schedule manipulation are studied. Preventative and corrective mitigation strategies are proposed and simulated in a co-simulation platform that comprises a network simulator (ns-3), a distribution grid simulator (GridLAB-D), a distributed network protocol 3 (DNP3) implementation (opendnp3) and a co-simulation coupling engine (HELICS). Six fictitious attack scenarios and their mitigation strategies are simulated on the two feeders of the City of Riverside Public Utilities, California.