A common source of water leaks in a freezer is the unit's ice maker. Check your ice maker to ensure it is operating properly. Empty the ice catch or tray and allow the unit to make new ice. Check to see that the tray fills with water and does not overflow. Inspect the back of the unit and ensure that the ice maker's water feeder lines are properly attached to the ice maker and the lines are undamaged.
In the back of the freezer, typically in one of the corners, you'll find a small drain for the self-defrost mechanism. These drains can become filled with debris from food stored in the freezer, and cause overflows. Check to ensure the drain is clean, and wipe the area down with a damp sponge.
In addition to the drain itself, the drain lines of the self-defrost mechanism can become clogged with ice. Pour a small amount of warm water down the defrost drain to free up any accumulated ice clogs in the lines. If the water sits in the drain or overflows, the lines might be clogged with debris and need to be cleaned or replaced. The drain lines can typically be accessed by removing the back panel of the freezer, and detaching them from the drain pan on the bottom of the unit and the drain cups on the freezer floor.
In the bottom of the freezer is a condensation or drain pan that catches the condensation accumulated by the unit, and the water removed from inside the freezer by the self-defrost mechanism. Over time, these pans can become clogged with dirt and debris from your kitchen floor, causing overflows. Remove the front grill on your unit and slide the pan out of its housing according to maintenance instructions in your unit's user manual. Wipe the pan down before re-installing. Double check to make sure the pan is seated properly and is sitting level, to prevent future overflows.