Rear Bumper loose?

Thanks for the good ideas. The pass side is the same, with the stamped square hole. From under the car absolutely no access to the corner. The other nuts are all good and tight.

However I did look from the trunk, and beholden, the pass side has a round hole. However it is about 3 inches higher than the square hole on the bumper. But if I take a long screwdriver, I can angle it into the hole from the outer square hole. So is something , like a bracket, supposed to be connected to the hole in the trunk? Now on the driver side in the trunk, some damage I guess as there is no hole and it looks like someone did a shabby job of fixing the metal. Although at this point the trunk floor is pretty badly rusted out. Sewe the pics for the bumper. How do I use that hole to help shore up the sides on the bumper?rear bumper - 1.jpg rear bumper - 2.jpg rear bumper - 3.jpg