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Blocking SMTP authentication brute force attacks using Fail2Ban - Fail2Ban can be used to block brute force attacks against your mail server. The attackers are blocked by their source IP using iptables. Although it doesn't block SMTP attacks by default, Fail2Ban can be configured to do so.Blocking SMTP authentication brute force attacks using [[Fail2Ban]] - Fail2Ban can be used to block brute force attacks against your mail server. The attackers are blocked by their source IP using iptables. Although it doesn't block SMTP attacks by default, Fail2Ban can be configured to do so.First, you need to install Fail2Ban. For Redhat/Fedora use yum.{{:Linux fail2ban Installation}} yum install fail2banCentOS: fail2ban is not available from CentOS. It will have to be manually downloaded. You can get it from EPEL, the Fedora repository. ==== configure ==== wget http://mirror.pnl.gov/epel//6/i386/fail2ban-0.8.11-2.el6.noarch.rpm rpm -ih --percent fail2ban-0.8.11-2.el6.noarch.rpmYou might have some dependencies to install, like yum install gamin-python wget http://mirror.pnl.gov/epel//6/i386/python-inotify-0.9.1-1.el6.noarch.rpm rpm -ih --percent python-inotify-0.9.1-1.el6.noarch.rpmThese are the most common 2 needed for CentOS users. Get them and any others possibly needed then try to install fail2ban again.ALL LINUX DISTRIBUTIONS - Fail2ban is written in Python, thus no compilation is required. You can even run Fail2ban without installing it. It can always be obtained directly from http://www.fail2ban.orgConfiguration for Fail2ban on a Redhat/Fedora/CentOS style distribution. This is using fail2ban with dovecot 2.x (versions 2 and above) - filtering and pattern matching.==== configure ====#configuration files: ./fail2ban#regex filters: ./fail2ban/filter.d#action file (do/block): ./fail2ban/action.d===== fail2ban.conf =====First edit the dovecot.conf filter file. vi ./fail2ban/[[sample-filter.d|filter.d]]Now modify the configuration fileNext edit the postfix-sasl.conf and iptables-multiport-tcp.conf action files. vi /etc/fail2ban/fail2ban.conf vi ./fail2ban/filter.d/[[sample-postfix-sasl.conf|postfix-sasl.conf]] vi ./fail2ban/action.d/[[sample-iptables-multiport-tcp.conf|iptables-multiport-tcp.conf]]Set the path to the log file.Do not directly edit jail.conf. Comments in jail.conf clearly warn against modifications in jail.conf. Put your customizations in a jail.local file or a jail.d/customisation.local cp ./fail2ban/jail.conf ./fail2ban/jail.local vi ./fail2ban/[[sample-jail.local|jail.local]]Configuration Parameters:Important Configuration Parameters:*filter: Refers to the appropriate filter file in "/etc/fail2ban/filter.d".*filter: Refers to the appropriate filter file in "./fail2ban/filter.d".===== jail.conf / jail.local ===== ignoreip = 127.0.0.1 192.168.254.0/24 Comments in jail.conf clearly warn against modifications in jail.conf. Put your customizations in a jail.local file or a jail.d/customisation.local cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local vi /etc/fail2ban/jail.localSet the IP addresses of trusted hosts for fail2ban to ignore. Replace the 192x non-routable with the address of your machine or network. You can also add other trusted networks. Put your mom's IP address in there because sometimes she gets her password wrong more than 3 times in a row!