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I have a fail2ban configured like below:

  • block the ip after 3 failed attempts
  • release the IP after 300 sec timeout

This works perfectly and I want to keep it this way such that a valid user gets a chance to retry the login after the timeout. Now, I want to implement a rule where if same IP is been detected as attack and blocked, unblocked 5 times, permanently block the IP and never unblock again. Can this be achieved with fail2ban alone or I need to write my own script to do that?

I am doing this in centos.

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It's a rather silly idea - the more rules you add to iptables the slower it gets. – symcbean Aug 7 '12 at 13:19
Appreciate your comment but what I need is an answer and not a suggestion. Thanks anyway. – BTR Naidu Aug 7 '12 at 13:29
Sometimes the right answer to "how do I do X" is "don't do X". – ceejayoz Feb 20 '13 at 16:08
up vote 17 down vote accepted

There is no default feature or a setting within fail2ban to achieve this. But, you are probably looking for setting up fail2ban to monitor its own log file. It is a two step process...

Step 1

We could need to create a filter to check for BAN's in the log file (fail2ban's log file)

Step 2

We need to define the jail, similar to the following...

enabled = true
filter = fail2ban
action = iptables-allports[name=fail2ban]
logpath = /path/to/fail2ban.log
# findtime: 1 day
findtime = 86400
# bantime: 1 year
bantime = 31536000

Technically, it is not a permanent block, but only blocks for a year (that we can increase too).

Anyway, for your question (Can this be achieved with fail2ban alone or I need to write my own script to do that?)... writing own script might work well. Setting up the script to extract the frequently banned IPs and then putting them into /etc/hosts.deny is what I'd recommend.

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Adding to this excellent answer... Depending on how logging and MaxAuthTries are configured for sshd_config, this could potentially only block 3 failed logins for a sshd "session" - not 3 failed logins provided. For example, by default an attacker could try ['pass1', 'pass2', 'pass3'] in a single session before sshd disconnects. Depending on how sshd is set to log, this could appear as 1, 2 or 3 attempts to fail2ban. – Jonathan Vanasco Apr 28 at 17:24

I believe if you put bantime = -1 in that config section, it is a permanent block.

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Indeed, setting bantime to any negative value is a permanent ban (as of Fail2Ban ver. 0.6.1 (2006/03/16)) – voretaq7 Mar 21 '13 at 16:41
adding -1 to settings made fail2ban unresponsive – Erdem Ece Nov 25 '15 at 11:55

Phil Hagen wrote an excellent article on this subject. "Permanently Ban Repeat Offenders With fail2ban".

His suggestion is the same as Pothi but provides a step by step guide.

This included:

  • separate ban list by jail (ip.blocklist.ssh,
  • ban lists autoloaded if service restart (main advantage of this method imho)
  • email notification if repeater engaged.
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To expand on Chin's answer this is pretty simple. Just edit the 2 settings in /etc/fail2ban/jail.local to match your preferences.

 # ban time in seconds. Use -1 for forever. Example is 1 week.
 bantime  = 604800
 # number of failures before banning
 maxretry = 5
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