This paper investigates cyber-attacks compromising the data integrity of 100% inverter-interfaced islanded microgrids featuring an energy storage system (ESS), a wind turbine generator (WTG), a photovoltaic system (PV) and controllable loads. The ESS operates as the isochronous generator, responsible for forming the microgrid voltage and frequency, whereas the WTG and PV distributed energy resources (DER) operate in maximum-power-point-tracking (MPPT) mode. Mitigation solutions in the form of supplementary power control loops, employed on the power-electronic interfaced DERs are proposed in order to enhance the resilience of the microgrid to large voltage deviations resulting from cyber-attacks compromising data integrity. In the event where the supplementary control is no longer capable of compensating for the cyber-induced power mismatch, a load management scheme is proposed to curtail non-critical loads and prevent the microgrid voltage from collapsing. Simulation results validate the effectiveness of the proposed schemes on a 25 kV inverter-based microgrid benchmark.