Linux Iptables Firewall Shell Script For Standalone Server

A shell script on iptables rules for a webserver (no need to use APF or CSF) just run this script from /etc/rc.local and you are done. Save following script as /root/scripts/fw.start:

#!/bin/bash
# A Linux Shell Script with common rules for IPTABLES Firewall.
# By default this script only open port 80, 22, 53 (input)
# All outgoing traffic is allowed (default - output)
# -------------------------------------------------------------------------
# Copyright (c) 2004 nixCraft project <http://cyberciti.biz/fb/>
# This script is licensed under GNU GPL version 2.0 or above
# -------------------------------------------------------------------------
# This script is part of nixCraft shell script collection (NSSC)
# Visit http://bash.cyberciti.biz/ for more information.
# -------------------------------------------------------------------------
 
IPT="/sbin/iptables"
SPAMLIST="blockedip"
SPAMDROPMSG="BLOCKED IP DROP"
 
echo "Starting IPv4 Wall..."
$IPT -F
$IPT -X
$IPT -t nat -F
$IPT -t nat -X
$IPT -t mangle -F
$IPT -t mangle -X
modprobe ip_conntrack
 
[ -f /root/scripts/blocked.ips.txt ] && BADIPS=$(egrep -v -E "^#|^$" /root/scripts/blocked.ips.txt)
 
PUB_IF="eth0"
 
#unlimited
$IPT -A INPUT -i lo -j ACCEPT
$IPT -A OUTPUT -o lo -j ACCEPT
 
# DROP all incomming traffic
$IPT -P INPUT DROP
$IPT -P OUTPUT DROP
$IPT -P FORWARD DROP
 
if [ -f /root/scripts/blocked.ips.txt ];
then
# create a new iptables list
$IPT -N $SPAMLIST
 
for ipblock in $BADIPS
do
   $IPT -A $SPAMLIST -s $ipblock -j LOG --log-prefix "$SPAMDROPMSG"
   $IPT -A $SPAMLIST -s $ipblock -j DROP
done
 
$IPT -I INPUT -j $SPAMLIST
$IPT -I OUTPUT -j $SPAMLIST
$IPT -I FORWARD -j $SPAMLIST
fi
 
# Block sync
$IPT -A INPUT -i ${PUB_IF} -p tcp ! --syn -m state --state NEW  -m limit --limit 5/m --limit-burst 7 -j LOG --log-level 4 --log-prefix "Drop Sync"
$IPT -A INPUT -i ${PUB_IF} -p tcp ! --syn -m state --state NEW -j DROP
 
# Block Fragments
$IPT -A INPUT -i ${PUB_IF} -f  -m limit --limit 5/m --limit-burst 7 -j LOG --log-level 4 --log-prefix "Fragments Packets"
$IPT -A INPUT -i ${PUB_IF} -f -j DROP
 
# Block bad stuff
$IPT  -A INPUT -i ${PUB_IF} -p tcp --tcp-flags ALL FIN,URG,PSH -j DROP
$IPT  -A INPUT -i ${PUB_IF} -p tcp --tcp-flags ALL ALL -j DROP
 
$IPT  -A INPUT -i ${PUB_IF} -p tcp --tcp-flags ALL NONE -m limit --limit 5/m --limit-burst 7 -j LOG --log-level 4 --log-prefix "NULL Packets"
$IPT  -A INPUT -i ${PUB_IF} -p tcp --tcp-flags ALL NONE -j DROP # NULL packets
 
$IPT  -A INPUT -i ${PUB_IF} -p tcp --tcp-flags SYN,RST SYN,RST -j DROP
 
$IPT  -A INPUT -i ${PUB_IF} -p tcp --tcp-flags SYN,FIN SYN,FIN -m limit --limit 5/m --limit-burst 7 -j LOG --log-level 4 --log-prefix "XMAS Packets"
$IPT  -A INPUT -i ${PUB_IF} -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP #XMAS
 
$IPT  -A INPUT -i ${PUB_IF} -p tcp --tcp-flags FIN,ACK FIN -m limit --limit 5/m --limit-burst 7 -j LOG --log-level 4 --log-prefix "Fin Packets Scan"
$IPT  -A INPUT -i ${PUB_IF} -p tcp --tcp-flags FIN,ACK FIN -j DROP # FIN packet scans
 
$IPT  -A INPUT -i ${PUB_IF} -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP
 
# Allow full outgoing connection but no incomming stuff
$IPT -A INPUT -i eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPT -A OUTPUT -o eth0 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
 
# Allow ssh
$IPT -A INPUT -p tcp --destination-port 22 -j ACCEPT
 
# allow incomming ICMP ping pong stuff
$IPT -A INPUT -p icmp --icmp-type 8 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
$IPT -A OUTPUT -p icmp --icmp-type 0 -m state --state ESTABLISHED,RELATED -j ACCEPT
 
# Allow port 53 tcp/udp (DNS Server)
$IPT -A INPUT -p udp --dport 53 -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
$IPT -A OUTPUT -p udp --sport 53 -m state --state ESTABLISHED,RELATED -j ACCEPT
 
$IPT -A INPUT -p tcp --destination-port 53 -m state --state NEW,ESTABLISHED,RELATED  -j ACCEPT
$IPT -A OUTPUT -p tcp --sport 53 -m state --state ESTABLISHED,RELATED -j ACCEPT
 
# Open port 80
$IPT -A INPUT -p tcp --destination-port 80 -j ACCEPT
##### Add your rules below ######
 
##### END your rules ############
 
# Do not log smb/windows sharing packets - too much logging
$IPT -A INPUT -p tcp -i eth0 --dport 137:139 -j REJECT
$IPT -A INPUT -p udp -i eth0 --dport 137:139 -j REJECT
 
# log everything else and drop
$IPT -A INPUT -j LOG
$IPT -A FORWARD -j LOG
$IPT -A INPUT -j DROP
 
exit 0

How do I install and use this script?

Type the following command as root server:
# mkdir /root/scripts
# cd /root/scripts
# wget http://bash.cyberciti.biz/dl/381.sh.zip
# wget http://bash.cyberciti.biz/dl/151.sh.zip
# unzip 381.sh.zip
# unzip 151.sh.zip
# mv 381.sh start.fw
# mv 151.sh stop.fw
# chmod +x *.fw
Now edit firewall as per your requirements:
# vi /root/scripts/start.fw
Install firewall:
# echo '/root/scripts/start.fw' >> /etc/rc.local

How do I start firewall from a shell prompt?

# /root/scripts/start.fw

How do I stop firewall from a shell prompt?

# /root/scripts/stop.fw

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