This, and the other thousand exploits against JavaScript's security model that have dribbled out at a steady rate over the last 20 years, is why "HTML5 apps" are a bad idea.
Theoretically, there's no intrinsic problem that anyone can point to. In practice, when the world has spent 20 years trying to plug the holes and is still failing several times per month, there comes a moment when rational players ought to conclude that there perhaps is an intrinsic problem and it is simply that we don't know what it is.