Diagnosis
Water is leaking from the pod holder assembly, usually because the silicone gasket (a small black ring) is damaged, dirty, or out of place.
How to Fix It
Unplug the machine. Let it cool. Remove the pod holder by pulling it straight up. Look inside the empty cavity in the machine. At the bottom, you'll see a flat black rubber/silicone gasket. Carefully lift it out with your fingernail. Rinse it under warm water and inspect it for nicks, tears, or warping. Clean the groove it sits in. If the gasket looks good, reseat it firmly. If it's damaged, you need a replacement—search for 'Keurig K-Express pod holder gasket'.
If That Didn't Work
The leak might be from the pod holder itself. Check for a hairline crack, especially around the rim or the latch. If it's cracked, you need a new pod holder assembly.
Heads Up
Don't use the machine while it's leaking. Water inside the electronics is a short-circuit risk. And never use a knife or sharp tool to pry out the gasket—you'll cut it.