I cannot recall any CIA agent being able to infiltrate KGB.
American intelligence services are not as effective as the legend says. Like a guy wrote in a recent book, CIA has a “legacy of ashes”.
Unlike the old MVD or KGB, the CIA has never been effective with deep cover penetration agents inserted into another country’s spy service. I don’t know of any successful penetrations either. Of course, I wouldn’t want or expect to know of any for that matter.
CIA case officers try to ‘turn’ foreign nationals already in the service of their country. We’ve had some successes there.