Check Arno's iptables firewall, as an option...

Isn't ailen's firewall generator script a bit outdated and no good to use on a 5.x kernel?

http://www.slackware.com/~alien/efg/

Hmm

Maybe a firewall is outdated.

Back in simpler times, Nigerian spam was from people trying to move around millions in imaginary money and wanted to use your account to 'rest' it in; Chinese spam obviously knew that European males were all poorly equipped for sexual relationships, and they needed medical assistance to extend what little they had. You blocked Nigerian & Chinese IPs with a firewall, and it was job done.

These days, there's no safe IP ranges, because hackers springboard from compromised boxes in innocuous places (e.g. Solar Winds) and we really need something else.

No firewall alone was ever a complete solution, nor could ever be.

Depending on the host role, securing it should always involve multiple layers steps and precautions.

A firewall should be viewed as an additional layer to the fortress - the outer ditch, figuratively speaking.