DIAGNOSIS You've got a seal failure. Either the silicone gasket on the brew basket lid is torn/misaligned, or the basket holder itself isn't locking fully into place.
FIX 1) Unplug the machine and let it cool. 2) Remove the brew basket and inspect the round, black silicone gasket on the underside of the flip-top lid. Clean any grounds off it and look for nicks or warping. 3) Also check the orange silicone seal on the basket holder (the part you twist). Make sure it's seated in its groove. 4) When you reassemble, ensure the basket holder clicks firmly into place with a full quarter-turn. You shouldn't be able to lift it without twisting back first.
IF THAT DIDN'T WORK The leak might be coming from above. Overfilling the reservoir beyond the MAX line can cause water to overflow internally and drip down. Always fill with the reservoir seated in the machine so you see the true level.
HEADS UP Never force the basket holder closed if it feels resistant. A misaligned thread can crack the plastic mounting post, which is a much bigger repair.