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Block Brute-Force Attempts on Ubuntu Linux - Fail2Ban

Fail2ban operates by blocking selected IP addresses that may belong to hosts that are trying to breach the system's security. It determines the hosts to be blocked by monitoring log files (e.g. /var/log/pwdfail, /var/log/auth.log, etc.) and bans any host IP that makes too many login attempts or performs any other unwanted action within a time frame defined by the administrator.

Fail2ban is typically set up to unban a blocked host within a certain period, so as to not "lock out" any genuine connections that may have been temporarily misconfigured. However, an unban time of several minutes is usually enough to stop a network connection being flooded by malicious connections, as well as reducing the likelihood of a successful dictionary attack.

Fail2ban can perform multiple actions whenever an abusive IP is detected: update Netfilter/iptables firewall rules, or alternatively TCP Wrapper's hosts.deny table, to reject an abuser's IP address; email notifications; or any user-defined action that can be carried out by a Python script. The standard configuration ships with filters for Apache, Lighttpd, sshd, vsftpd, qmail, Postfix and Courier Mail Server.

Fail2Ban Installation:
To install fail2ban, type the following in the terminal:
sudo apt-get install fail2ban 
Fail2Ban should be correctly installed now. Just type following command to see if everything is all right.
fail2ban-client -h
Fail2Ban Configuration:
Fail2ban configuration files can be found under /etc/fail2ban
First, Set the IPs you want fail2ban to ignore, adjust the ban time (in seconds) and maximum number of user attempts:
# "ignoreip" can be an IP address, a CIDR mask or a DNS host
ignoreip =
bantime  = 600
maxretry = 3
Next, you need to configure the service ...
By default, some sections are inserted as templates. You must enable the sections of interest and adapt to your local configuration. Here is an example of the ssh section:
enabled  = true
port     = ssh
filter   = sshd
logpath  = /var/log/auth.log
maxretry = 4
 * The section ssh is enabled, in short, your ssh server is now protected.
 * The filter sshd.conf in sub-directory filter.d will be processed.
 * The banaction = iptables-multiport described above in the jail.conf file will be used and iptables-multiport.conf (sub-directory action.d) will be executed if the outcome of the filter process is true.
 * The log file to be scanned by the filter is auth.log.

Once done all the configuration setting has been done, restart fail2ban using following command
sudo /etc/init.d/fail2ban restart


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