I would be very unsurprised if it turned out to be McCain that leaked it.
And you would be surprised if it were the CIA or others in the Obama administration that leaked it?
BTW, the "dossier" was leaked to many media outlets months ago.
What is new is that the IC leaked to CNN and others that the dossier was in the classified Trump briefing. That is why CNN decided to start reporting on the dossier's existence.