While this is most likely a Microsoft issue, it is possible that Safari installed itself in such a way to access Ring 0.
While I suppose you could argue that it's theoretically possible that's what happened here, the fact is, it's not what happened here. Microsoft is scrambling to fix their vulnerability, instead of pointing a finger back at Apple, so we know for sure it's a Microsoft issue. Otherwise, MS would have a field day with Apple's application error.
I can't say with authority that Windows Safari stays out of Ring 0 -- it might throw some driver in the kernel, I don't know offhand. But an IFRAME tag causing a large memory request is not a Ring 0 kernel kind of a problem. No application memory allocation request should ever cause a bluescreen. And Microsoft will find it and fix it, they're bright folks.
Nice try, no dice.