I'd like to limit connections to specific ports in order to protect my server against DOS attacks. Is there a way to do this with CSF Firewall?
Yes, CSF provides a way to limit concurrent connections to specific ports. As an example, the following may be added to the configuration file to limit port 80 and port 443 to 5 connections.
CONNLIMIT = "80;5,443;5"
You can read more about this in the CSF Readme.