Fail2ban

Fail2ban scans log files (e.g. /var/log/apache/error_log) and bans IPs that show the malicious signs – too many password failures, seeking for exploits, etc. Generally Fail2Ban is then used to update firewall rules to reject the IP addresses for a specified amount of time, although any arbitrary other action (e.g. sending an email) could also be configured. Out of the box Fail2Ban comes with filters for various services (Apache, Dovecot, Ssh, Postfix, etc).

Fail2Ban is able to reduce the rate of incorrect authentications attempts however, it cannot eliminate the risk that weak authentication presents. To improve the security, open the access to service only for secure networks using the firewall.

Installation

Install from the Software Center or use the command line:

yum install nethserver-fail2ban

Settings

Fail2ban is configurable in the security category of the server-manager. Most of settings can be changed in the Configuration tab, only really advanced settings must be configured by the terminal. The Ban status tab displays the statistic and the banned IPs.

Jails

A jail is enabled and start to protect a service when you install a new module, the relevant jail (if existing) is automatically activated after the package installation.

All jails can be disabled individually in the Jails settings.

Number of attempts
Number of matches (i.e. value of the counter) which triggers ban action on the IP.
Time span
The counter is set to zero if no match is found within “findtime” seconds.
Ban Time
Duration for IP to be banned for.
Recidive jail is perpetual
When an IP goes several time in jail, the recidive jail bans it for a much longer time. If enabled, it is perpetual.

Network

Allow bans on the LAN
By default the failed attempts from your Local Network are ignored, except when you enabled the option.
IP/Network Whitelisting
IP listed in the text area will be never banned by fail2ban (one IP per line). Network could be allowed in the Trusted-Network panel.

Email

Send email notifications
Enable to send administrative emails.
Administrators emails
List of email addresses of administrators (one address per line).
Notify jail start/stop events
Send email notifications when a jail is started or stopped.

Unban IP

IPs are banned when they are found several times in log, during a specific find time. They are stored in a database to be banned again each time your restart the server or the service. To unban an IP you can use the Ban status tab.

Tools

Fail2ban-client

Fail2ban-client is part of the fail2ban rpm, it gives the state of fail2ban and all available jails:

fail2ban-client status

To see a specific jail :

fail2ban-client status sshd

To see which logfiles are monitored for a jail:

fail2ban-client get nginx-http-auth logpath

Fail2ban-listban

Fail2ban-listban counts the IPs currently and totally banned in all activated jails, at the end it shows the IPs which are still banned by shorewall.

fail2ban-listban

Fail2ban-regex

Fail2ban-regex is a tool which is used to test the regex on you logs, it is a part of fail2ban software. Only one filter is allowed per jail, but it is possible to specify several actions, on separate lines.

The documentation is readable at the fail2ban project.

fail2ban-regex /var/log/YOUR_LOG /etc/fail2ban/filter.d/YOUR_JAIL.conf --print-all-matched

You can also test custom regex directly:

fail2ban-regex /var/log/secure '^%(__prefix_line)s(?:error: PAM: )?[aA]uthentication (?:failure|error) for .* from <HOST>( via \S+)?\s*$'

Fail2ban-unban

Fail2ban-unban is used to unban an IP when the ban must be removed manually.

fail2ban-unban <IP>

You can use also the built-in command with fail2ban-client:

fail2ban-client set <JAIL> unbanip <IP>

Whois

If you desire to query the IP whois database and obtain the origin of the banned IP by email, you could Install the whois rpm.