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<title>Using UFW as a Firewall – LandChad.net</title>
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<header><h1>Using UFW as a Firewall</h1></header>
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<p>
<strong>Uncomplicated Firewall</strong> (UFW) is a front-facing program for the more involved <code>iptables</code> firewall program installed in most GNU/Linux distributions.
If you're reading this, I assume you know the basic steps on how to use a Linux shell and how to install software for your server.
Otherwise, I recommend following <a href="nginx.html">Setting Up a Web Server</a>.
</p>
<h2 id="how-to-get-it">How to Get It</h2>
<p>
If you followed <a href="nginx.html#firewall">the basic setup course</a>, then you know that Vultr already installed <code>ufw</code> for you.
If you don't use Vultr, then you can install it on a Debian system by running in a remote shell:
</p>
<pre><code>sudo apt-get update && sudo apt-get install ufw</code></pre>
<p>
The first command checks to see what packages can be installed, and the second command installs <code>ufw</code>.
It's strung together by a <code>&&</code> to run the second command as long as the first succeeded.
</p>
<h2 id="first-time-setup">First-Time Setup</h2>
<p>
<code>ufw</code> is an administration program, so you will need root access to use it.
To make sure you don't have to keep typing <code>sudo</code> in all your commands, you can login to the root user by running:
</p>
<pre><code>sudo su -</code></pre>
<p>I'll assume you're in a root account from now on, but otherwise, remember to prepend all <code>ufw</code> commands with <code>sudo</code>.</p>
<p>You can check the status of <code>ufw</code> right now by running:</p>
<pre><code>ufw status</code></pre>
<p>Without any changes, it should report back <code>Status: inactive</code>. Let's set it up so that only connections to SSH (standardized at port 22) are allowed in, and then enable the firewall:</p>
<aside>
<strong>Careful!</strong> Enabling <code>ufw</code> without allowing SSH will block you from remoting to your server.
Double-check that you have allowed SSH, and if you have changed the default SSH port, put in <em>that</em> number instead.
And then double-check again.
</aside>
<pre><code>ufw default deny incoming # block all incoming connections by default
ufw allow in ssh # or: ufw allow in 22
ufw enable</code></pre>
<aside>
<code>ufw</code> has an internal list of protocols applications, and the ports used by them.
In this case, it knwos SSH is on port 22.
We'll go more in detail how to view all protocols <code>ufw</code> knows about.
By default, when you allow an incoming port, it allows that port both on IPv4 and IPv6.
</aside>
<p>
With the firewall enabled and allowing only SSH in, all other ports are prortected from incoming requests.
To view all your rules, run:
</p>
<pre><code>ufw status verbose</code></pre>
<p>A firewall that allows to connect to SSH and their website may look like:</p>
<pre><code>Status: active
Logging: on (low)
Default: deny (incoming), allow (outgoing), deny (routed)
New profiles: skip
To Action From
-- ------ ----
22 (SSH) ALLOW IN Anywhere
80,443/tcp (WWW Full) ALLOW IN Anywhere
22 (SSH (v6)) ALLOW IN Anywhere (v6)
80,443/tcp (WWW Full (v6)) ALLOW IN Anywhere (v6)</code></pre>
<p>If you want to delete e.g. the 'WWW Full' rule, run:</p>
<pre><code>ufw delete allow in 'WWW Full'
ufw reload</pre></code>
<h2 id="enabling-common-services">Enabling Common Services</h2>
<p>
You have blocked all incoming ports but SSH, which means no outsiders would be able to access other services, like an email server or your website.
You should look at the ports your services are open on and enable them individually.
Here is a list of a few common services:
</p>
<h3>Websites: HTTP and HTTPS</h3>
<pre><code>ufw allow in 'WWW Full'
ufw reload</code></pre>
<h3>Email: IMAP, POP3, and SMTP</h3>
<pre><code>ufw allow in IMAPS
ufw allow in POP3
ufw allow in SMTP
ufw allow in 'Postfix SMTPS'
ufw allow in 'Mail Submission'
ufw reload</pre></code>
<h3>Everything Else</h3>
<p>You can view all applications <code>ufw</code> knows about by running:</p>
<pre><code>ufw app list</code></pre>
<h2 id="fine-tuning-rules">Fine-Tuning Rules</h2>
<p>Instead of denying all ports by default, you may want to deny (ignores incoming requests) or reject (explicitly tells requests they're not allowed):</p>
<pre><code>ufw default allow in
ufw deny in <strong>PORT</strong>
ufw reject in <strong>PORT</strong>
ufw reload</code></pre>
<p>You can add rules to comments to remember what they are there for:</p>
<pre><code>ufw allow in <strong>PORT</strong> comment 'Secret SSH'
ufw reload
ufw status verbose</code></pre>
<p>Output:</p>
<pre><code>To Action From
-- ------ ----
<strong>PORT</strong> ALLOW IN Anywhere # Secret SSH
<strong>PORT</strong> (v6) ALLOW IN Anywhere (v6) # Secret SSH</pre></code>
<p>To deny outgoing ports:</p>
<pre><code>ufw deny out <strong>PORT</strong></code></pre>
<p>Ratelimiting is useful to protect against brute-force login attacks, like in SSH. Only IPv4 is supported for now. Enable it by running:</p>
<pre><code>ufw limit <strong>PORT</strong>/tcp</code></pre>
<p>To blocklist IP addresses:</p>
<pre><code>ufw deny from <strong>IP_ADDRESS</strong></code></pre>
<p>To read more what you can do with <code>ufw</code>, run:</p>
<pre><code>man ufw</code></pre>
<h2 id="further-reading">Further Reading</h2>
<ul>
<li><a href="https://wiki.ubuntu.com/UncomplicatedFirewall">Ubuntu Wiki: UncomplicatedFirewall</a></li>
<li><a href="https://help.ubuntu.com/community/Gufw">Gufw (Graphical UFW)</a></li>
<li><code>man ufw</code></li>
</ul>
<strong>Contributor</strong> - <a href="https://shunter.xyz">shunter.xyz</a>
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