Barton Gellman wrote about this very thing happening to his iPad (remote jailbreak/root) when he was working with Snowden, in his book Dark Mirror.
The leveraging of Android malware for espionage (corporate and military both) is well-documented in the media.
Do you know of any instances where this happened with devices that can be rooted? (Computers, most Android phones, iPhones vulnerable to Checkm8)