Thought everyone knew this. Yes, the CIA installled one of their own, then the FBI cracked him open with the first FISA warrant. The FBI asked the CIA if Page was working for them. CIA answered “yes”. Why would the FBI ask this question? FBI altered the CIA’s “yes” response changing it to a “no” on the FISA application.
Obama made sure with one of his final acts in office.
https://www.theguardian.com/world/2017/jan/12/obama-us-intelligence-greater-access-warrantless-data-foreign-targets