doc/pages/02.administer/50.troubleshooting/05.fail2ban/fail2ban.md

title	template	taxonomy	routes
IP address unban	docs	category docs	default /fail2ban

Fail2Ban is an intrusion prevention software that protects computer servers against brute-force attacks. It monitors certain logs and will ban IP addresses that show brute-force-like behavior.

In particular, Fail2Ban monitors SSH connection attempts. After 5 failed SSH connection attempts, Fail2Ban will ban the IP address from connecting via SSH for 10 minutes. If this address fails several times, it might get banned for a week.

Unban an IP address

To unblock an IP address, you must first access your server by some means (for example from another IP address or from another internet connection than the banned one).

Then, look at the Fail2Ban’s log to identify in which jail the IP address has been banned:

sudo tail /var/log/fail2ban.log
2019-01-07 16:24:47 fail2ban.filter  [1837]: INFO    [sshd] Found 11.22.33.44
2019-01-07 16:24:49 fail2ban.filter  [1837]: INFO    [sshd] Found 11.22.33.44
2019-01-07 16:24:51 fail2ban.filter  [1837]: INFO    [sshd] Found 11.22.33.44
2019-01-07 16:24:54 fail2ban.filter  [1837]: INFO    [sshd] Found 11.22.33.44
2019-01-07 16:24:57 fail2ban.filter  [1837]: INFO    [sshd] Found 11.22.33.44
2019-01-07 16:24:57 fail2ban.actions [1837]: NOTICE  [sshd] Ban 11.22.33.44
2019-01-07 16:24:57 fail2ban.filter  [1837]: NOTICE  [recidive] Ban 11.22.33.44

Here, the 11.22.33.44 IP address has been banned in the sshd and recidive jails.

Then deban the IP address with the following commands:

sudo fail2ban-client set sshd unbanip 11.22.33.44
sudo fail2ban-client set recidive unbanip 11.22.33.44

Whitelist an IP address

If you don’t want a "legitimate" IP address to be blocked by YunoHost anymore, then you have to fill it in the whitelist of the jail configuration file.

When updating the Fail2Ban software, the original /etc/fail2ban/jail.conf file is overwritten. So it is on a new dedicated file that we will store the changes. They will thus be preserved over time.

1. Start by creating the new jail configuration file which will be called yunohost-whitelist.conf:

   sudo touch /etc/fail2ban/jail.d/yunohost-whitelist.conf
   

2. Edit this new file with your favorite editor:

   sudo nano /etc/fail2ban/jail.d/yunohost-whitelist.conf
   

3. Paste the following content into the file and adapt the IP address XXX.XXX.XXX.XXX:

   ! Keep the 127.0.0.1/8, it corresponds to the server internal communication system

   [DEFAULT]
   
   ignoreip = 127.0.0.1/8 XXX.XXX.XXX.XXX
   #                      ^ Add your IP address or DNS host here
   #                        you can put more than one, separated by a space
   

4. You should get end up with something like this if you have added two ip addresses (ipv4 and ipv6)

   [DEFAULT]
   
   ignoreip = 127.0.0.1/8 203.0.113.4 2001:DB8::1
   

5. Save the file and reload the Fail2Ban configuration:

   sudo fail2ban-client reload
   

6. Check that the configuration has been applied as expected:

   1. You should have this result

      root@sambain:/etc/nginx# fail2ban-client get sshd ignoreip
      These IP addresses/networks are ignored:
      |- 127.0.0.0/8
      |- 2001:db8::1
      |- XXX.XXX.XXX.XXX
      `- 203.0.113.4
      

   2. If there is an error with your change, you could end up with something like this:

      sudo fail2ban-client get sshd ignoreip
      These IP addresses/networks are ignored:
      |- 127.0.0.0/8
      |- #<=
      |- the
      |- IP
      |- address
      |- (you
      |- can
      |- put
      |- more
      |- than
      |- one
      |- separated
      |- by
      |- a
      |- space)
      |- that
      |- you
      |- want
      |- to
      |- whitelist
      |- 203.0.113.4
      |- XXX.XXX.XXX.XXX
      `- 2001:db8::1
      

      And you will need to fix it or revert your changes as Fail2ban could fail

      For the curious, it was because of a comment ;

Congratulations, no more risks of banning yourself from your own YunoHost server!