How To Setup fail2ban Ubuntu 18.04

Fail2ban is an application that parses the system logs looking for signs of an automated attack.

When an attack attempted is identified, Fail2ban adds a rule to iptables to block the IP address of the attacker. This block can be set either for a specific period of time or permanently. fail2ban focuses on SSH attacks.

Since fail2ban 0.9, the bans are persistent. fail2ban maintains a database at /var/lib/fail2ban/fail2ban.sqlite3.

fail2ban: Installation

sudo apt-get install fail2ban

fail2ban: Configuration

The /etc/fail2ban/fail2ban.conf contains the default configuration. It is a good practice to copy this file to /etc/fail2ban/fail2ban.local. In fail2ban .local files override .conf files

cp /etc/fail2ban/fail2ban.conf /etc/fail2ban/fail2ban.local

The /etc/fail2ban/jail.conf file enables fail2ban configuration for SSH. Again, it is a good practice to copy this file to /etc/fail2ban/jail.local.

fail2ban: Whitelist IPs

To make an IP ignored by fail2ban, use the ignoreip setting:

ignoreip = 127.0.0.1/8 1.1.1.1

fail2ban: Ban Time

Use bantime setting to set the number of seconds for which an IP is banned. If set to a negative number, the ban is permanent.

fail2ban: Retry Time / Amount

Use findtime to set the number of seconds between login attempts before a ban is set. It is used in conjunction with maxretry which sets how many attempts can be made to access the server from a specific IP before it is banned.

fail2ban: SSH Settings

By default in fail2ban only SSH settings are enabled.

[ssh]

enabled  = true
port     = ssh
filter   = sshd
logpath  = /var/log/auth.log
maxretry = 6

For port, if using the default 22 port, the service name can be used. Otherwise, for non-traditional ports, use the port number explicitly.

fail2ban: Regex

fail2ban uses regular expressions (regex) to parse log files in order to identify potential attacks. fail2ban uses Python’s regex implementation.

Use fail2ban-regex to check if your custom filter is working.

fail2ban-regex /var/www/html/logs/access.log /etc/fail2ban/filter.d/wordpress.conf

fail2ban: Command Line Client

fail2ban provides a command-line (CLI) tool fail2ban-client.

  • start - start the fail2ban server and all defined jails.
  • reload - reload the fail2ban configuration
  • reload <jail> - reload a specific jail configuration
  • stop - stop the fail2ban server
  • status - show the fail2ban status and active jails

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