The problem with CoreGui is that any indexing of it with a roblox script will error with a permission error. However, I found out that exploiters can parent the Gui under game:GetService'CoreGui' and operate it fine.
This is a problem because now we have a blind spot that exploiters can use, and even if we had a way to find and delete their guis, how would we test it out with Roblox scripts?
Currently erroring code
local a=game:GetService'CoreGui';
a.DescendantAdded:Connect(function(b) --> error
end);

1 comment
I don't think you can do anything to that area. I think it's locked.