fail2ban nginx 404 400 403 444 filter /etc/fail2ban/filter.d/nginx-4xx.conf enable

jail.conf

# to enable  this filter add to  jail.conf following (/etc/fail2ban/jail.conf)
# Thanks to -> TheBarret

[nginx-4xx]
enabled = true
port = http,https
logpath = /var/log/nginx/access.log
maxretry = 3

nginx.conf

# vim /etc/fail2ban/filter.d/nginx-4xx.conf 

[Definition]
failregex = ^<HOST>.*"(GET|POST).*" (404|444|403|400) .*$
ignoreregex =

head -18 /etc/fail2ban/jail.conf
#
# WARNING: heavily refactored in 0.9.0 release.  Please review and
#          customize settings for your setup.
#
# Changes:  in most of the cases you should not modify this
#           file, but provide customizations in jail.local file,
#           or separate .conf files under jail.d/ directory, e.g.:
#
# HOW TO ACTIVATE JAILS:
#
# YOU SHOULD NOT MODIFY THIS FILE.
#
# It will probably be overwritten or improved in a distribution update.
#
# Provide customizations in a jail.local file or a jail.d/customisation.local.
# For example to change the default bantime for all jails and to enable the
# ssh-iptables jail the following (uncommented) would appear in the .local file.
# See man 5 jail.conf for details.