“According to one current and one former U.S. government official speaking on the condition of anonymity, Darroch repeatedly leaked classified U.S. intelligence information, including highly classified information, to a journalist for a U.S.-based media outlet.”
So a current government official is leaking this information to the Washington Examiner.
Britain’s ambassador, Sir Kim Darroch was the leaker.
How did he get the info?
Best bet would Brennan and our SOS at that time.