this post was submitted on 06 Oct 2023
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If you allow the whole subnet you might as well not use a firewall. Your router has one and port forwarding is disabled by default.
Your isp firewall uses nat, and a hacked isp gateway or some other device that had ports forwarded to it are the most likely things to be reaching into your network. They’ll be on that subnet.
Yes, they’re giving “very simplistic” and also demonstrating how to deny and add access in multiple ways.
It’s also not uncommon to do things like that. The default firewall config in Fedora is wide open for every port above 1024.
I set up a rule last night to allow SSH access from any device on my subnet, is it a good idea to add a separate rule blocking SSH from my router? I’ve already set up SSH with public key authentication so in theory there aren’t many devices that can access it but the firewall restriction seemed like a good idea
If you are worried that an attacker may have compromised your router and that key auth is not secure enough, then yes it would make sense.
I move ssh to a non-default port, only allow key based auth and install fail2ban. This is enough for me. It protects against automated attacks hitting port 22 and prevents brute force.
I don’t think my router has been compromised and I think it’s pretty unlikely it will be, but the extra rule seems pretty trivial to set up so if there are no downsides I may as well! I have already changed the SSH port and disabled password login. I’ll look into fail2ban, might be worth it if it’s relatively simple to set up!
Yeah, I kind of agree. Unless this is a mobile device pretty much all traffic will come from within your subnet. I often deny incoming from my gateway (i.e. router) and poke holes as necessary.