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#+date: <2021-01-07 Thu 00:00:00>
#+title: Configuring Uncomplicated Firewall (ufw) on Ubuntu Servers
#+description: Stepwise instructions for installation, configuration, enabling, and management of the Uncomplicated Firewall utility to secure network interfaces on Ubuntu server environments.
#+slug: ufw
#+filetags: :firewall:security:ufw:
* Uncomplicated Firewall
Uncomplicated Firewall, also known as ufw, is a convenient and
beginner-friendly way to enforce OS-level firewall rules. For those who
are hosting servers or any device that is accessible to the world (i.e.,
by public IP or domain name), it's critical that a firewall is properly
implemented and active.
Ufw is available by default in all Ubuntu installations after 8.04 LTS.
For other distributions, you can look to install ufw or check if there
are alternative firewalls installed already. There are usually
alternatives available, such as Fedora's =firewall= and the package
available on most distributions: =iptables=. Ufw is considered a
beginner-friendly front-end to iptables.
[[https://gufw.org][Gufw]] is available as a graphical user interface
(GUI) application for users who are uncomfortable setting up a firewall
through a terminal.
* Getting Help
If you need help figuring out commands, remember that you can run the
=--help= flag to get a list of options.
#+begin_src sh
sudo ufw --help
#+end_src
* Set Default State
The proper way to run a firewall is to set a strict default state and
slowly open up ports that you want to allow. This helps prevent anything
malicious from slipping through the cracks. The following command
prevents all incoming traffic (other than the rules we specify later),
but you can also set this for outgoing connections, if necessary.
#+begin_src sh
sudo ufw default deny incoming
#+end_src
You should also allow outgoing traffic if you want to allow the device
to communicate back to you or other parties. For example, media servers
like Plex need to be able to send out data related to streaming the
media.
#+begin_src sh
sudo ufw default allow outgoing
#+end_src
* Adding Port Rules
Now that we've disabled all incoming traffic by default, we need to open
up some ports (or else no traffic would be able to come in). If you need
to be able to =ssh= into the machine, you'll need to open up port 22.
#+begin_src sh
sudo ufw allow 22
#+end_src
You can also issue more restrictive rules. The following rule will allow
=ssh= connections only from machines on the local subnet.
#+begin_src sh
sudo ufw allow proto tcp from 192.168.0.0/24 to any port 22
#+end_src
If you need to set a rule that isn't tcp, just append your connection
type to the end of the rule.
#+begin_src sh
sudo ufw allow 1900/udp
#+end_src
* Enable ufw
Now that the firewall is configured and ready to go, you can enable the
firewall.
#+begin_src sh
sudo ufw enable
#+end_src
A restart may be required for the firewall to begin operating.
#+begin_src sh
sudo reboot now
#+end_src
* Checking Status
Now that the firewall is enabled, let's check and see what the rules
look like.
#+begin_src sh
sudo ufw status numbered
#+end_src
#+begin_src txt
Status: active
To Action From
-- ------ ----
[ 1] 22 ALLOW IN Anywhere
[ 2] 22 (v6) ALLOW IN Anywhere (v6)
#+end_src
* Deleting Rules
If you need to delete a rule, you need to know the number associated
with that rule. Let's delete the first rule in the table above. You'll
be asked to confirm the deletion as part of this process.
#+begin_src sh
sudo ufw delete 1
#+end_src
* Managing App Rules
Luckily, there's a convenient way for installed applications to create
files that ufw can easily implement so that you don't have to search and
find which ports your application requires. To see if your device has
any applications with pre-installed ufw rules, execute the following
command:
#+begin_src sh
sudo ufw app list
#+end_src
The results should look something like this:
#+begin_src txt
Available applications:
OpenSSH
Samba
plexmediaserver
plexmediaserver-all
plexmediaserver-dlna
#+end_src
If you want to get more information on a specific app rule, use the
=info= command.
#+begin_src sh
sudo ufw app info plexmediaserver-dlna
#+end_src
You'll get a blurb of info back like this:
#+begin_src txt
Profile: plexmediaserver-dlna
Title: Plex Media Server (DLNA)
Description: The Plex Media Server (additional DLNA capability only)
Ports:
1900/udp
32469/tcp
#+end_src
You can add or delete app rules the same way that you'd add or delete
specific port rules.
#+begin_src sh
sudo ufw allow plexmediaserver-dlna
#+end_src
#+begin_src sh
sudo ufw delete RULE|NUM
#+end_src
* Creating App Rules
If you'd like to create you own app rule, you'll need to create a file
in the =/etc/ufw/applications.d= directory. Within the file you create,
you need to make sure the content is properly formatted.
For example, here are the contents my =plexmediaserver= file, which
creates three distinct app rules for ufw:
#+begin_src config
[plexmediaserver]
title=Plex Media Server (Standard)
description=The Plex Media Server
ports=32400/tcp|3005/tcp|5353/udp|8324/tcp|32410:32414/udp
[plexmediaserver-dlna]
title=Plex Media Server (DLNA)
description=The Plex Media Server (additional DLNA capability only)
ports=1900/udp|32469/tcp
[plexmediaserver-all]
title=Plex Media Server (Standard + DLNA)
description=The Plex Media Server (with additional DLNA capability)
ports=32400/tcp|3005/tcp|5353/udp|8324/tcp|32410:32414/udp|1900/udp|32469/tcp
#+end_src
So, if I wanted to create a custom app rule called "mycustomrule," I'd
create a file and add my content like this:
#+begin_src sh
sudo nano /etc/ufw/applications.d/mycustomrule
#+end_src
#+begin_src config
[mycustomrule]
title=My Custom Rule
description=This is a temporary ufw app rule.
ports=88/tcp|9100/udp
#+end_src
Then, I would just enable this rule in ufw.
#+begin_src sh
sudo ufw allow mycustomrule
#+end_src
|
