CNN is staking their reputation on breaking this story. It was Tapper, Jim Sciutto and Carl Bernstein who broke it, the former two being two of their most respected people, and Bernstein being one of the original reporters who broke Watergate. They're not journalistic nobodies.
But this wealth of information has been known about in the media for a LONG time, and has been reported on before. CNN is NOT reporting that everything in the Buzzfeed dossier is true, in fact they said it's unverified. But as has been said, they learned that our intelligence trusted the source agent and his sources to be credible enough to transfer his info into a two-page report that was given to POTUS, PEOTUS, and a "Gang of 8" select Congress leaders/intel committee heads.
There's reason to believe the FBI is looking into this. Comey would NOT answer when asked today if they're actively investigating campaigns contacting Russia, and he quoted a longstanding tradition to not comment on open investigations. I took that to mean yes. And also, this: