Diagnosis
The defrost drain tube is clogged. When the freezer defrosts, water should flow down this tube to a drain pan at the bottom. A clog causes it to back up and overflow into the fridge.
How to Fix It
Remove all food and shelves from the fresh food section. Locate the drain hole at the back of the compartment, near the bottom. Use a turkey baster or syringe to flush warm water mixed with a little baking soda into the drain. Use a long, flexible brush or pipe cleaner to gently clear debris. Pour a cup of hot water down the drain to ensure it flows freely to the drain pan at the rear bottom of the unit.
If That Didn't Work
The drain tube may be frozen shut where it passes through the freezer wall. Unplug the unit for 24 hours to allow a complete thaw. You can also use a hairdryer on a low, cool setting to warm the tube area at the back of the freezer interior.
Heads Up
Do not use wire hangers or sharp objects to clear the drain. You can puncture the plastic liner or disconnect the tube. Use only soft, flexible tools.