Yeah, this one's common. It's almost always an overfilled reservoir or a bad seal. First, check you're not filling past the 12-cup line. If you are, that water has to go somewhere, and it's out the bottom.
If the fill level is correct, the internal water tube or a seal is probably cracked. Unplug it. Wipe it dry. Look for visible cracks around the water reservoir inside the unit. There's no safe way to open it up yourself to check further. If you see a crack or the leak persists with correct filling, it's time for a new machine.