DIAGNOSIS Water is overflowing from the internal tank, usually because the drain plug at the back isn't fully sealed or the water inlet valve is stuck open.
FIX First, check the obvious: make sure the rubber drain plug on the back is pushed in all the way and seated tightly. It can work loose during cleaning. If that's secure, the issue is likely internal. Unplug it, empty all water, and tip it over a towel. Check if the internal overflow tube (visible once you remove the top lid/cover) is cracked or disconnected.
IF THAT DIDN'T WORK The float valve that controls water intake might be stuck. You can try gently tapping the side of the unit to free it, but if the leak persists, the valve assembly probably needs replacement.
HEADS UP Never overfill the water reservoir past the max line. Excess water has nowhere to go but out the overflow and straight to the bottom of the unit.