ConfigServer Community Forum

I get that CSF acts as a firewall for the server and can thus help to protect against attacks on the server.

However, will it help prevent a DDoS attack on a domain/website (specifically a forum) residing on that server?

Yes, indeed. Search csf.conf for "D?DOS", especially:
SECTION:Port Flood Settings
SECTION:Connection Tracking
SECTION:Distributed Attacks

Thank you.