mikaela.github.io/blog/_posts/2015-06-12-ufw.md

This post describes my UFW config and is here so I find it from somewhere and with hope that I am told if someone notices something terriby insecure here and is able to offer suggestions. This probably will never be perfect.

Having firewall is important as you aren’t always in your trusted home network (that can also be broken into especially if you have WLAN) and with IPv6 your devices have public IPv6 addresses. Theoretically your router should include a firewall, but at least the Huawei mobile broadband routers or MiFis don’t include one (and I might be annoyed by it enough to disable it anyway and configure everything on host level if it was my network).

Threat model: service I am not aware of or that I accidentally make listen wider than intended, with UFW I am aware of what ports are allowed. I assume any mobile host is going to move randomly and while some whitelists (especially link-local and IPv4 LANs) will overlap and possibly allow access, it’s still better than being open to the internet and overlay networks that I have interacted with recently.

This post first has list of commands, then explanations that won’t be repeated with IPvX ranges.

ufw allow 22/tcp
ufw default deny incoming
ufw default allow outgoing
systemctl enable ufw && systemctl start ufw
ufw enable
ufw reject 113/tcp
#ufw allow from 192.168.0.0/16 to any port 123 proto udp
ufw allow from fe80::/10 to any port 123 proto udp
#ufw allow from 192.168.8.0/24 to any port 631 proto tcp
ufw allow from fe80::/10 to any port 631
#ufw allow from 192.168.8.0/24 to any port 5353 proto udp
ufw allow from fe80::/10 to any port 5353 proto udp
#ufw allow from <static:Yggdrasil:IPv6> to any port 5900
ufw allow 6771/udp
ufw allow from fe80::/10 to any port 9001 proto udp
ufw allow 60000:61000/udp

• 22 TCP/ssh — Allow acces to SSHd you don’t want to lock yourself out.
  • previously I used ufw limit but it seems to be too oversensitive, just use SSHGuard.
• Deny incoming connections unless the port has been whitelisted.
• Allow all outgoing connections, keeping list of authorized ports would be too much for me.
• Start ufw on boot and now (I am not sure if this step is required, but better safe than sorry).
• Put the firewall in force.
• 113 TCP/ident — Tell “Connection refused” to whoever tries to reach port 113. This makes ident checking IRC servers connect faster as they don’t have to timeout. If you run shell server (for IRC purpouses) you should allow this instead. And if you don’t use IRC or don’t care about having to wait for the check to timeout, don’t do this as you may leave yourself visible to random port scanners.
• 123 UDP/NTP - syncing time between local hosts
• 631 both/cups — Allow access to cups for printer sharing from 192.168.8.xxx
  • fe80:://10 is link-local address existing everywhere IPv6 is enabled, check your ip addr or on Windows ipconfig /all for fun.
• 5353 UDP/mdns/Avahi — used for .local addresses.
• 5900 — VNC port at least for krfb kdrc (KDE Remote Desktop server & client). I tend to only allow it from specific Yggdrasil address(es).
• 6771/udp — Bittorrent Local Peer Discovery
• 9001/udp — Yggdrasil automatic peering port only on link-local.
• 60000:61000 UDP/mosh — I feel this is the most insecure part of this setup and there should be something bettter instead of this. As something evil could run and listen on these ports.

If some host doesn’t run some of the mentioned service, it’s not open in the firewall.

KDE Connect which seems painful enough to list separately and doesn’t seem to work IPv6-only or I am too impatient.

#ufw allow from 192.168.8.0/24 to any port 1714:1764 proto tcp
#ufw allow from 192.168.8.0/24 to any port 1714:1764 proto udp
ufw allow from fe80::/10 to any port 1714:1764 proto tcp
ufw allow from fe80::/10 to any port 1714:1764 proto udp

EXTRA:

If you need WLAN tethering, edit /etc/ufw/sysctl.conf and:

ufw route allow in on enp3s0 out on wlp2s0
ufw route allow in on wlp2s0 out on enp3s0

I am not sure if both rules are required, enp3s0 is the ethernet interface and wlp2s0 the wireless one. I think it would make sense for only the first to be required.

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Last updated: 2020-10-26 | GitHub changelog | Blesmrt Gitea changelog