fail2ban ufw ipv6 fix

[ugjka]

          I also had a problem that a IPv6 attacker was not blocked. First check your current ufw version:

$ ufw version

If you have >= 0.36 you can either adapt /etc/fail2ban/action.d/ufw.conf or create a new file /etc/fail2ban/action.d/ufw-custom.conf with the necessary change:

$ diff ufw.conf ufw-custom.conf 
17c17
<             ufw insert <insertpos> <blocktype> from <ip> to <destination> $app
---
>             ufw prepend <blocktype> from <ip> to <destination> $app
23,26d22
< # Option: insertpos
< # Notes.:  The position number in the firewall list to insert the block rule
< insertpos = 1
< 

and use that in /etc/fail2ban/jail.local.

Originally posted by @blinkeye in fail2ban/fail2ban#2331 (comment)