Actually it is mostly Buffon's fault after I watched the replay. If you think the keeper should be catching the ball at his penalty spot from a through ball from that far away then you're insane.
Next up it's Chiellini's fault but at least he has an excuse of the rain + Ronaldo on his shoulder.
If you tell me Buffon should catch that ball on his penalty spot instead of the top of the box, which avoids the entire situation, then you have never played the sport seriously.