In this article, the resilience of a coordinated control system for a set of PV-based distributed energy resources (DERs) against false data injection (FDI) attacks is evaluated. The evaluation is performed using a functional mock-up interface (FMI)-compatible cosimulation platform which enables the interaction of multi-domain simulators (EMTP, MATLAB/Simulink, and NS-3). The cosimulation platform permits rigorous analysis of cybersecurity through detailed modeling of all system components. The DER coordinated control and communication systems implemented on the IEEE-34 bus benchmark consist of measurement, control and monitoring components including substation central controller, DER local controllers, synchrophasor network and advanced metering infrastructure (AMI). Some DERs are equipped with an energy storage system (ESS) and coordinated by the central control unit in order to correct voltage disturbances resulting from the intermittent solar photovoltaic (PV) generation. The FDI attack targets the AMI system and aims at manipulating the load profile messages reported by the smart meter collector, thus yielding a central control failure. To detect the attacks and mitigate their impacts, a neural network-based algorithm is proposed and incorporated in the central control unit. The effectiveness of the proposed detection and mitigation algorithm is confirmed through simulations using the proposed FMI-compatible cosimulation platform.