They certainly have agents inside Russia. Been causing problems since the war began. And it shouldn't be that hard to buy cheap drones and rig them with explosives.
Right. I just can't see them flying drones from the Ukrainian side of the border and get all the way to Moscow. I tend to think agents in Russia or maybe a small contingent of Ukranian special forces infiltrating and hitting from a closer spot.
My suspicion is agents within Russia trying to stir up fear there.