###############################
# SIMPLE FIREWALL RULES FOR IPTABLES
#
# By Pekka Helenius (~Fincer), 2018
#
# These rules are intended to be used
# without UFW. If you have additional
# firewall settings in your system/iptables, 
# take care adapting these rules in to your 
# current firewall ruleset.
#
# I do not take responsibility of breaking
# your working firewall configuration!
#
############
#
# The rules in this file do the following:
#
# A) do not respond to incoming ping requests
# Can be used as a replacement for sysctl 'net.ipv4.icmp_echo_ignore_all=1' setting
#
# B) drop all incoming traffic by default, except for
# SSH, HTTP and HTTPS protocols
#
# C) start dropping packets if connection cycle is too intense
# from one client. This setting may be useful against port scanners.
#
# Ruleset C) by Anthony Maro:
# https://www.ossramblings.com/using_iptables_rate_limiting_to_prevent_portscans
#
############
#
# INSTALLATION
#
# NOTE: Intended to be used without UFW or any other
# firewall settings!!
#
# 1) Recommended: Remove existing firewall front-ends such as UFW from your system 
#
# 2) Delete all previous firewall rules by issuing
#    sudo iptables --flush && sudo iptables --delete-chain
#
# 3) Check output of 'iptables -S'. It should be
#    -P INPUT ACCEPT
#    -P FORWARD ACCEPT
#    -P OUTPUT ACCEPT
#
# 4) In this file, change SSH, HTTP and HTTPS port numbers to fit your server environment
#
#    Default values are:
#
#        SSH: 22
#        HTTP: 80
#        HTTPS: 443
#
# Default setting for C) is 10 maximum connection attempts in 30 seconds
# Adapt the values to your server environment.
#
# 5) Save this file to /etc/iptables/iptables.rules
#
# 6) Check that it is used by 'iptables-restore' command
#
# In systemd environments, check the value of 'ExecStart' and 'ExecReload'
# in file /lib/systemd/system/iptables.service. The entries should be as follows:
#
#    ExecStart=/usr/bin/iptables-restore /etc/iptables/iptables.rules
#    ExecReload=/usr/bin/iptables-restore /etc/iptables/iptables.rules
#
# 7) Once you have double-checked that the parameters in this file are correct (step 4), run
#    sudo iptables-restore /etc/iptables/iptables.rules
#    sudo systemctl enable iptables && sudo systemctl start iptables
#
# 8) Check that the rules have been applied:
#    sudo iptables -S
#
#
###############################
# USEFUL LINKS
#
# https://www.thegeekstuff.com/scripts/iptables-rules
# https://gist.github.com/thomasfr/9712418
#
###############################
#
# BEGINNING OF FIREWALL RULES
#

*filter

###############################
# DEFAULT POLICY FOR THIS CHAIN - DROP ALL INPUT TRAFFIC
#
# THIS IS A DANGEROUS SETTING. IF YOU DROP ALL INCOMING
# CONNECTIONS, MAKE SURE YOU HAVE ACCEPTED AT LEAST SSH CONNECTION INPUT BELOW
# OTHERWISE YOU WILL BE LOCKED OUT FROM THE SERVER!
#
# DO NOT USE 'REJECT' BECAUSE IT GIVES A RESPONSE TO A HOSTILE CLIENTS (PORT SCANNERS)
# INSTEAD, DROP INCOMING PACKETS AND DO NOT GIVE RESPONSE AT ALL
#

-P INPUT DROP

###############################
# WE ARE NOT A ROUTER, WE DROP ALL (NON-EXISTENT) FORWARD CONNECTIONS
#

-P FORWARD DROP

###############################
# BY DEFAULT, ALL OUTGOING TRAFFIC FROM THE SERVER IS ACCEPTED
#

-P OUTPUT ACCEPT

###############################
# DROP ALL INCOMING PING REQUESTS
#

-A INPUT -p icmp --icmp-type echo-request -j DROP

###############################
# ALLOW LOOPBACK CONNECTIONS
#

-A INPUT -i lo -j ACCEPT
#-A OUTPUT -o lo -j ACCEPT

###############################
# ALLOW INCOMING SSH CONNECTIONS
#

-A INPUT -p tcp --dport 22 -m state --state NEW -j ACCEPT
#-A OUTPUT -p tcp --sport 22 -m state --state NEW -j ACCEPT

###############################
# ALLOW INCOMING HTTP/HTTPS CONNECTIONS
#

-A INPUT -p tcp -m multiport --dports 80,443 -m state --state NEW -j ACCEPT
#-A OUTPUT -p tcp -m multiport --sports 80,443 -m state --state NEW -j ACCEPT

###############################
# ALLOW ESTABLISHED AND RELATED CONNECTIONS
#

-A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
#-A OUTPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT

###############################
# RULESET C)
#
# IF 10 NEW CONNECTIONS TO ANY PORT WITHIN 30 SECONDS IS REQUESTED BY A CLIENT, START DROPPING PACKETS FOR THE CLIENT
#
# SHOULD FREEZE NMAP AND OTHER PORT SCANNERS
#
# Source: https://www.ossramblings.com/using_iptables_rate_limiting_to_prevent_portscans

-A INPUT -i $IFACE -p tcp -m state --state NEW -m recent --set --name DEFAULT --mask 255.255.255.255 --rsource
-A INPUT -i $IFACE -p tcp -m state --state NEW -m recent --update --seconds 30 --hitcount 10 --name DEFAULT --mask 255.255.255.255 --rsource -j DROP

###############################

COMMIT

# END OF FIREWALL RULES