How to Install Fail2ban on CentOS 7

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Most Linux servers offer an SSH login via port 22 for remote administration purposes. While connecting to your server through SSH can be very secure, the SSH daemon itself is a service that must be exposed to the Internet to function properly. This comes with some inherent risk and offers a vector of attack for would-be assailants.

Any service that is exposed to the network is a potential target in this way. If you pay attention to application logs for these services, you will often see repeated, systematic login attempts that represent brute-force attacks by users and bots alike.

The most common solution to prevent this kind of attacks is using key-based SSH authentication. The other is move the port to some random high-port. But how if you still need to use password-based SSH authentication on port 22?

A service called Fail2ban can mitigate this problem by creating rules that automatically alter your iptables firewall configuration based on a predefined number of unsuccessful login attempts. This will allow your server to respond to illegitimate access attempts without intervention from you.

In this guide, we'll cover how to install and use Fail2ban on a CentOS 7 server.

Install Fail2ban on CentOS 7

While Fail2ban is not available in the official CentOS package repository, it is packaged for the EPEL project. EPEL, standing for Extra Packages for Enterprise Linux, can be installed with a release package that is available from CentOS:

$ sudo yum install epel-release

It will ask you to proceed with installation.

Transaction Summary
================================================================================
Install  1 Package

Total download size: 15 k
Installed size: 24 k
Is this ok [y/d/N]: y

Next step is to install the fail2ban:

$ sudo yum install fail2ban

Again, press 'y' and Enter when asked to continue with installation.

Transaction Summary
================================================================================
Install  1 Package (+12 Dependent packages)

Total download size: 1.5 M
Installed size: 5.4 M
Is this ok [y/d/N]: y

Please note that you might be asked to proceed with importing new GPG key like so:

Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
Importing GPG key 0x352C64E5:
 Userid     : "Fedora EPEL (7) <[email protected]>"
 Fingerprint: 91e9 7d7c 4a5e 96f1 7f3e 888f 6a2f aea2 352c 64e5
 Package    : epel-release-7-11.noarch (@extras)
 From       : /etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
Is this ok [y/N]: y

No worries, just press 'y' and Enter. Once the installation has finished, use systemctl to enable the fail2ban service:

$ sudo systemctl enable fail2ban

If you're familiar with CentOS 6, the equivalent command is:

$ sudo chkconfig fail2ban on

Configure SSH Jail

The Fail2ban service keeps its configuration files in the /etc/fail2ban directory. There, you can find a file with default values called jail.conf. Since this file may be overwritten by package upgrades, we shouldn't edit it in-place. Instead, we'll write a new file called sshd.conf under directory /etc/fail2ban/jail.d/.

Let's begin by writing a very simple version of sshd.conf. Open a new file using vi (or your editor of choice):

$ sudo vi /etc/fail2ban/jail.d/sshd.conf

Paste the following code:

[sshd]
enabled = true
port = ssh
logpath = %(sshd_log)s
maxretry = 3
bantime = 31536000 # One year

Exit and save the new file (in vi/vim, press Esc to enter command mode, and then continue with :wq). Now we can restart the fail2ban service using systemctl:

$ sudo systemctl start fail2ban

The systemctl command should finish without any output. In order to check that the service is running, we can use fail2ban-client:

$ sudo fail2ban-client status
Status
|- Number of jail: 1
`- Jail list: sshd

Final Words

I hope that you now know how to install fail2ban on CentOS 7. If you run into any issues or have any feedback feel free to drop a comment below.

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