Fail2ban scans various textual log files and bans IP that makes too many password failures by updating firewall rules to reject the IP address.
First, install python2-pyinotify so that Fail2ban can detect modification to the log files:
# pacman -S python2-pyinotify
# pacman -S fail2ban
If you want Fail2ban to send an email when someone has been banned, you have to configure SSMTP (for example). You will also have to install to get some information about the attacker.
# pacman -S whois
Use the service unit fail2ban.service, refer to systemd for instructions.
journaldlogging. This is because it parses textual files like
journalduses its own binary format. You must use
syslog-ngor similar to have textual logging.
Currently, fail2ban requires to run as root, therefore you may wish to consider some additional hardening on the process with systemd. Ref:systemd for Administrators, Part XII
For added security consider limiting fail2ban capabilities by specifying
CapabilityBoundingSet in the drop-in configuration file for the provided
[Service] CapabilityBoundingSet=CAP_DAC_READ_SEARCH CAP_NET_ADMIN CAP_NET_RAW
In the example above,
CAP_DAC_READ_SEARCH will allow fail2ban full read access, and
CAP_NET_RAW allow setting of firewall rules with iptables. Additional capabilities may be required, depending on your fail2ban configuration. See
man capabilities for more info.
Also considering limiting file system read and write access, by using ReadOnlyDirectories and ReadWriteDirectories, again under the under
[Service] section. For example:
ReadOnlyDirectories=/ ReadWriteDirectories=/var/run/fail2ban /var/spool/postfix/maildrop
In the example above, this limits the file system to read-only, except for
/var/run/fail2ban for pid and socket files, and
/var/spool/postfix/maildrop for postfix sendmail. Again, this will be dependent on you system configuration and fail2ban configuration. Note that adding
/var/log is necessary if you want fail2ban to log its activity.
/etc/fail2ban/jail.conf and modify the ssh-iptables section to enable it and configure the action.
If your firewall is iptables:
[ssh-iptables] enabled = true filter = sshd action = iptables[name=SSH, port=ssh, protocol=tcp] sendmail-whois[name=SSH, firstname.lastname@example.org, email@example.com] logpath = /var/log/auth.log maxretry = 5
If your firewall is shorewall:
[ssh-shorewall] enabled = true filter = sshd action = shorewall sendmail-whois[name=SSH, firstname.lastname@example.org, email@example.com] logpath = /var/log/auth.log maxretry = 5
/etc/shorewall/shorewall.confotherwise the rule added to ban an IP address will affect only new connections.
Also do not forget to add/change:
/etc/ssh/sshd_config. Else, password failures are not logged correctly.