Disallow request epoch to be out of bound

beacon-chain/rpc/validator/assignments.go

@@ -110,6 +110,11 @@ func (vs *Server) StreamDuties(req *ethpb.DutiesRequest, stream ethpb.BeaconNode
 // Compute the validator duties from the head state's corresponding epoch
 // for validators public key / indices requested.
 func (vs *Server) duties(ctx context.Context, req *ethpb.DutiesRequest) (*ethpb.DutiesResponse, error) {
+	currentEpoch := helpers.SlotToEpoch(vs.TimeFetcher.CurrentSlot())
+	if req.Epoch > currentEpoch+1 {
+		return nil, status.Errorf(codes.InvalidArgument, "Request epoch can not be greater than next epoch %d", currentEpoch+1)
+	}
+
 	s, err := vs.HeadFetcher.HeadState(ctx)
 	if err != nil {
 		return nil, status.Errorf(codes.Internal, "Could not get head state: %v", err)