Russia already revealed Brennan's mole
Mikhailov of the FSB.
https://www.rferl.org/a/russia-sentences-cyberexperts-to-long-jail-terms-for-treason-/29791990.html
Though I also think Torschin is possible.
He ran the FSB, then central bank, and was Butinas handler.
Now retired.
https://www.bloomberg.com/news/articles/2018-11-30/nra-linked-russia-central-banker-retires-as-aide-nears-u-s-deal