Self-Hosted Main

As title says, i'm curious about the worst case scenario in which an attacker tries to hit my system.

The system configuration is the following: i have some services (important ones) accessible only trough VPN, like SSH (key-based auth only), Pihole...Others are publicly accessible, like Immich, Jellyfin (and so on...).Public ones are accessible via reverse proxy (Caddy) and protected by CrowdSec (which bans IPs outside my country and those failing auth 3 times).

What could happen if an attacker finds out a vulnerability on some public service? Would he be only able to access service's files (like an appropriate login), or delete/encrypt data (as some cases of blackmail) or even pull out and steal my data?
I'm wondering this because i want to know if CrowdSec+Docker (to preserve permissions on the system) is enough to secure a server.