Your defrost drain is clogged or frozen. You'll have to pull rear freezer panel off to get to it.
It'll be a hole below the evaporator (finned thing) that is meant to drain the water produced by defrost cycle, When it can't that water pools on bottom of freezer and leaks into fridge.
Easiest thing is to unplug and leave the doors open for 48 hours but you'll need a plan for all the melt water. We use steamers to speed this up. You may be able to crack the thick stuff on the freezer bottom into pieces after it has melted a little and remove to minimize how much liquid water you need to deal with.
After that all melts out try to pour hot water down that hole, if it doesn't drain you'll need t either let it thaw if it is still frozen or use air or water pressure to clear whatever the obstruction is. Or if you're lucky you can remove rear back panel and find a clog right there at point the tube hits the drain pan. Probably not though.