Sounds like a job for crowdsec. Basically fail2ban on steroids. They already have a ban scenario for attempts to exploit web application CVEs. While the default ssh scenario does not ban specific usernames, I'm pretty sure writing a custom one would be trivial (writing a custom parser+scenario for ghost cvs from no knowledge to fully deployed took me just one afternoon)
Another thing I like about crowdsec is the crowd sourced ban IPs. It's super nice you can preemptively ban IPs that are port-scanning/probing other people's servers.
It's also MIT licensed and uses less ram than fail2ban.
One way to do this would be set up crowdsec bouncers on each server but only run a single instance of the crowdsec daemon. Send all logs to the daemon and let it communicate with all the bouncers.