Linux : Using Fail2ban to Block Network Probes

Installing and Using Fail2ban On Debian and Ubuntu system

Make sure your package repositories and installed programs are up to date by issuing the following commands:


[email protected]:~$ sudo apt-get update
[sudo] password for kartook:

[email protected]:~$ sudo apt-get upgrade –show-upgraded

[email protected]:~$ sudo apt-get install python

[email protected]:~$ sudo apt-get install fail2ban

[email protected]:~$

Afterwards, you will find all fail2ban configuration files in the /etc/fail2ban directory, take a backup for future use .

[email protected]:~$ sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.conf.backup

[email protected]:~$ sudo cp /etc/fail2ban/fail2ban.conf /etc/fail2ban/fail2ban.conf.backup

—- FILE   START   HERE ——

# Fail2Ban configuration file.
#
# This file was composed for Debian systems from the original one
#   provided now under /usr/share/doc/fail2ban/examples/jail.conf
#   for additional examples.
#
# To avoid merges during upgrades DO NOT MODIFY THIS FILE
# and rather provide your changes in /etc/fail2ban/jail.local
#
# Author: Yaroslav O. Halchenko <[email protected]>
#
# $Revision: 281 $
#

# The DEFAULT allows a global definition of the options. They can be override
# in each jail afterwards.

[DEFAULT]

# “ignoreip” can be an IP address, a CIDR mask or a DNS host
#
########### HERE IS THE CHANGES WE NEED TO CONFIGURE THE IP ADDRESS MULTIPLE IP ADDRESS SEPARATED BY SPACE ##############
############## I AM USING SERVER IP ADDRESS : 192.168.100.10 192.168.100.252 #############

ignoreip = 127.0.0.1 192.168.100.10 192.168.100.252
bantime   = 600
maxretry = 3

# “backend” specifies the backend used to get files modification. Available
# options are “gamin”, “polling” and “auto”.
# yoh: For some reason Debian shipped python-gamin didn’t work as expected
#           This issue left ToDo, so polling is default backend for now
backend = polling

#
# Destination email address used solely for the interpolations in
# jail.{conf,local} configuration files.
destemail = [email protected]

#
# ACTIONS
#

# Default banning action (e.g. iptables, iptables-new,
# iptables-multiport, shorewall, etc) It is used to define
# action_* variables. Can be overriden globally or per
# section within jail.local file
banaction = iptables-multiport

# email action. Since 0.8.1 upstream fail2ban uses sendmail
# MTA for the mailing. Change mta configuration parameter to mail
# if you want to revert to conventional ‘mail’.
mta = sendmail

# Default protocol
protocol = tcp

#
# Action shortcuts. To be used to define action parameter

# The simplest action to take: ban only
action_ = %(banaction)s[name=%(__name__)s, port=”%(port)s”, protocol=”%(protocol)s]

# ban & send an e-mail with whois report to the destemail.
action_mw = %(banaction)s[name=%(__name__)s, port=”%(port)s”, protocol=”%(protocol)s] %(mta)s-whois[name=%(__name__)s, dest=”%(destemail)s”, protocol=”%(protocol)s]

# ban & send an e-mail with whois report and relevant log lines
# to the destemail.
action_mwl = %(banaction)s[name=%(__name__)s, port=”%(port)s”, protocol=”%(protocol)s] %(mta)s-whois-lines[name=%(__name__)s, dest=”%(destemail)s”, logpath=%(logpath)s]

# Choose default action.   To change, just override value of ‘action’ with the
# interpolation to the chosen action shortcut (e.g.   action_mw, action_mwl, etc) in jail.local
# globally (section [DEFAULT]) or per specific section
action = %(action_)s

#
# JAILS
#

# Next jails corresponds to the standard configuration in Fail2ban 0.6 which
# was shipped in Debian. Enable any defined here jail by including
#
# [SECTION_NAME] # enabled = true

#
# in /etc/fail2ban/jail.local.
#
# Optionally you may override any other parameter (e.g. banaction,
# action, port, logpath, etc) in that section within jail.local

[ssh]

enabled = true
port      = ssh
filter      = sshd
logpath   = /var/log/auth.log
maxretry = 6

# Generic filter for pam. Has to be used with action which bans all ports
# such as iptables-allports, shorewall
[pam-generic]

enabled = false
# pam-generic filter can be customized to monitor specific subset of ‘tty’s
filter      = pam-generic
# port actually must be irrelevant but lets leave it all for some possible uses
port = all
banaction = iptables-allports
port         = anyport
logpath   = /var/log/auth.log
maxretry = 6

[xinetd-fail]

enabled     = false
filter       = xinetd-fail
port           = all
banaction = iptables-multiport-log
logpath     = /var/log/daemon.log
maxretry   = 2

[ssh-ddos]

enabled = false
port       = ssh
filter   = sshd-ddos
logpath   = /var/log/auth.log
maxretry = 6

#
# HTTP servers
#

[apache]

enabled = false
port      = http,https
filter      = apache-auth
logpath = /var/log/apache*/*error.log
maxretry = 6

# default action is now multiport, so apache-multiport jail was left
# for compatibility with previous (<0.7.6-2) releases
[apache-multiport]

enabled     = false
port         = http,https
filter         = apache-auth
logpath     = /var/log/apache*/*error.log
maxretry   = 6

[apache-noscript]

enabled = false
port       = http,https
filter   = apache-noscript
logpath = /var/log/apache*/*error.log
maxretry = 6

[apache-overflows]

enabled = false
port       = http,https
filter   = apache-overflows
logpath = /var/log/apache*/*error.log
maxretry = 2

#
# FTP servers
#

[vsftpd]

enabled   = false
port       = ftp,ftp-data,ftps,ftps-data
filter     = vsftpd
logpath   = /var/log/vsftpd.log
# or overwrite it in jails.local to be
# logpath = /var/log/auth.log
# if you want to rely on PAM failed login attempts
# vsftpd’s failregex should match both of those formats
maxretry = 6

[proftpd]

enabled   = false
port       = ftp,ftp-data,ftps,ftps-data
filter     = proftpd
logpath   = /var/log/proftpd/proftpd.log
maxretry = 6

[wuftpd]

enabled   = false
port       = ftp,ftp-data,ftps,ftps-data
filter     = wuftpd
logpath   = /var/log/auth.log
maxretry = 6

#
# Mail servers
#

[postfix]

enabled   = false
port       = smtp,ssmtp
filter     = postfix
logpath   = /var/log/mail.log

[couriersmtp]

enabled   = false
port       = smtp,ssmtp
filter     = couriersmtp
logpath   = /var/log/mail.log

#
# Mail servers authenticators: might be used for smtp,ftp,imap servers, so
# all relevant ports get banned
#

[courierauth]

enabled   = false
port       = smtp,ssmtp,imap2,imap3,imaps,pop3,pop3s
filter     = courierlogin
logpath   = /var/log/mail.log

[sasl]

enabled   = false
port       = smtp,ssmtp,imap2,imap3,imaps,pop3,pop3s
filter     = sasl
# You might consider monitoring /var/log/warn.log instead
# if you are running postfix. See http://bugs.debian.org/507990
logpath   = /var/log/mail.log

# DNS Servers

# These jails block attacks against named (bind9). By default, logging is off
# with bind9 installation. You will need something like this:
#
# logging {
#         channel security_file {
#                 file “/var/log/named/security.log” versions 3 size 30m;
#                 severity dynamic;
#                 print-time yes;
#         };
#         category security {
#                 security_file;
#         };
# };
#
# in your named.conf to provide proper logging

# Word of Caution:
# Given filter can lead to DoS attack against your DNS server
# since there is no way to assure that UDP packets come from the
# real source IP
[named-refused-udp]

enabled   = false
port         = domain,953
protocol = udp
filter     = named-refused
logpath   = /var/log/named/security.log

[named-refused-tcp]

enabled   = false
port         = domain,953
protocol = tcp
filter     = named-refused
logpath   = /var/log/named/security.log

—-END OF FILE ——

Edit the configuration file /etc/fail2ban/jail.conf to set up blocking for various services.
SSH blocking will be enabled by default. To make sure you don’t accidentally lock yourself out of services, you can set the ignoreip variable to match your home or office connection’s IP address.
Set bantime to specify how long (in seconds) bans should last.
The maxretry variable specifies the default number of tries a connection may be attempted by any IP before a ban is put in place.

Fail2ban will monitor your log files for failed login attempts.
After an IP address has exceeded the maximum number of authentication attempts, it will be blocked at the network level and the event will be logged in /var/log/fail2ban.log

[email protected]:~$ sudo /etc/init.d/fail2ban restart

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