It has been known in the abstract, but AFAIK I was the first to publish a specific attack. (Not that I really claim that as much of an accomplishment. Sometimes it's hard to navigate the line between educating people and insulting their intelligence, particularly when it comes to security.)
Hasn't it always been known, since the beginning of this issue, that this was a penetrable 5c phone and thus a red herring for the FBI's request?