If you remove the bottom basket inside the freezer is there a build up of ice on the freezer floor?
Ok if theres ice under the freezer drawer then what you will find is the freezer drain channel is blocked up so when it goes into defrost mode the water pores over the top and into the freezer cabinet.
What you need to do is either empty the freezer and from there remove the back panel.
Behind there is the evaporator and under this is the drain channel.
Melt the ice in there and in the middle you will see the drain hole. Pore boiling water in there and poke the hole to defrost it all.
Once clear test it by poreing water in there and make sure it drains away ok.
If you don't want to go removing panels then you need to empty the freezer and turn it off for 24 hours and keep the freezer door open. This will allow the ice in there to melt away.
Once that's defrosted and the drain hole is clear this will cure the fault and stop it from leaking again.
If you need anymore info just get back to me.