There’s a chance it became classified, if for example the exploit depends on the existence of FBI managed tor nodes, and we aren’t ready to let everyone know that the feds are all over the onion network infra.
There have been a number of very strange arrests of tor users by FBI and other western special services. The one I remember was when they took down the hydra's (basically russian silk road) and doxed it's creators. The idea of tor being infiltrated by feds seems very logical, considering that Tor got a good reputation, and is, basically, a great honeypot. I'd consider it a real threat if I were a criminal. But are there any networks that are resistant to malicious nodes?