#!/bin/sh
# For debugging use iptables -v.
IPTABLES="/sbin/iptables"
MODPROBE="/sbin/modprobe"
RMMOD="/sbin/rmmod"
# Logging options.
#------------------------------------------------------------------------------
LOG="LOG --log-level debug --log-tcp-sequence --log-tcp-options"
LOG="$LOG --log-ip-options"
# Defaults for rate limiting
#------------------------------------------------------------------------------
RLIMIT="-m limit --limit 3/s --limit-burst 8"
# Load required kernel modules
#------------------------------------------------------------------------------
$MODPROBE ip_conntrack
$MODPROBE ip_conntrack_ftp
$MODPROBE ip_tables
$MODPROBE iptable_filter
$MODPROBE ipt_LOG
$MODPROBE ipt_state
# Disable IP forwarding.
echo 0 > /proc/sys/net/ipv4/ip_forward
# Enable IP spoofing protection *
for i in /proc/sys/net/ipv4/conf/*/rp_filter; do echo 1 > $i; done
# Protect against SYN flood attacks *
echo 1 > /proc/sys/net/ipv4/tcp_syncookies
# Ignore all incoming ICMP echo requests *
echo 0 > /proc/sys/net/ipv4/icmp_echo_ignore_all
# Ignore ICMP echo requests to broadcast *
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
# Log packets with impossible addresses. *
for i in /proc/sys/net/ipv4/conf/*/log_martians; do echo 1 > $i; done
# Don't log invalid responses to broadcast *
echo 1 > /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses
# Don't accept or send ICMP redirects. *
for i in /proc/sys/net/ipv4/conf/*/accept_redirects; do echo 0 > $i; done
for i in /proc/sys/net/ipv4/conf/*/send_redirects; do echo 0 > $i; done
# Don't accept source routed packets. *
for i in /proc/sys/net/ipv4/conf/*/accept_source_route; do echo 0 > $i; done
# Drop everything by default.*
$IPTABLES -P INPUT DROP
$IPTABLES -P FORWARD DROP
$IPTABLES -P OUTPUT DROP
# Set the nat/mangle/raw tables' chains to ACCEPT
$IPTABLES -t nat -P PREROUTING ACCEPT
$IPTABLES -t nat -P OUTPUT ACCEPT
$IPTABLES -t nat -P POSTROUTING ACCEPT
$IPTABLES -t mangle -P PREROUTING ACCEPT
$IPTABLES -t mangle -P INPUT ACCEPT
$IPTABLES -t mangle -P FORWARD ACCEPT
$IPTABLES -t mangle -P OUTPUT ACCEPT
$IPTABLES -t mangle -P POSTROUTING ACCEPT
# Delete all *
$IPTABLES -F
$IPTABLES -t nat -F
$IPTABLES -t mangle -F
# Delete all *
$IPTABLES -X
$IPTABLES -t nat -X
$IPTABLES -t mangle -X
# Zero all packets and counters. *
$IPTABLES -Z
$IPTABLES -t nat -Z
$IPTABLES -t mangle -Z
# LOG packets, then ACCEPT.
$IPTABLES -N ACCEPTLOG
$IPTABLES -A ACCEPTLOG -j $LOG $RLIMIT --log-prefix "ACCEPT "
$IPTABLES -A ACCEPTLOG -j ACCEPT
# LOG packets, then DROP.
$IPTABLES -N DROPLOG
$IPTABLES -A DROPLOG -j $LOG $RLIMIT --log-prefix "DROP "
$IPTABLES -A DROPLOG -j DROP
# LOG packets, then REJECT.
# TCP packets are rejected with a TCP reset.
$IPTABLES -N REJECTLOG
$IPTABLES -A REJECTLOG -j $LOG $RLIMIT --log-prefix "REJECT "
$IPTABLES -A REJECTLOG -p tcp -j REJECT --reject-with tcp-reset
$IPTABLES -A REJECTLOG -j REJECT
# Make It Even Harder To Multi-PING
$IPTABLES -A INPUT -p icmp -m limit --limit 1/s --limit-burst 2 -j ACCEPT
$IPTABLES -A INPUT -p icmp -m limit --limit 1/s --limit-burst 2 -j LOG --log-prefix PING-DROP:
$IPTABLES -A INPUT -p icmp -j DROP
$IPTABLES -A OUTPUT -p icmp -j ACCEPT
# First, drop all fragmented ICMP packets (almost always malicious).
$IPTABLES -A INPUT -p icmp --fragment -j DROPLOG
$IPTABLES -A OUTPUT -p icmp --fragment -j DROPLOG
$IPTABLES -A FORWARD -p icmp --fragment -j DROPLOG
# Allow all ESTABLISHED ICMP traffic.
$IPTABLES -A INPUT -p icmp -m state --state ESTABLISHED -j ACCEPT $RLIMIT
$IPTABLES -A OUTPUT -p icmp -m state --state ESTABLISHED -j ACCEPT $RLIMIT
# Allow some parts of the RELATED ICMP traffic, block the rest.
$IPTABLES -A INPUT -p icmp -m state --state RELATED -j RELATED_ICMP $RLIMIT
$IPTABLES -A OUTPUT -p icmp -m state --state RELATED -j RELATED_ICMP $RLIMIT
# Allow incoming ICMP echo requests (ping), but only rate-limited.
$IPTABLES -A INPUT -p icmp --icmp-type echo-request -j ACCEPT $RLIMIT
# Allow outgoing ICMP echo requests (ping), but only rate-limited.
$IPTABLES -A OUTPUT -p icmp --icmp-type echo-request -j ACCEPT $RLIMIT
# Drop any other ICMP traffic.
$IPTABLES -A INPUT -p icmp -j DROPLOG
$IPTABLES -A OUTPUT -p icmp -j DROPLOG
$IPTABLES -A FORWARD -p icmp -j DROPLOG
# Allow loopback interface to do anything. *
$IPTABLES -A INPUT -i lo -j ACCEPT
$IPTABLES -A OUTPUT -o lo -j ACCEPT
# Allow incoming connections related to existing allowed connections. *
$IPTABLES -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
# Allow outgoing connections EXCEPT invalid *
$IPTABLES -A OUTPUT -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
# We don't care about Milkosoft, Drop SMB/CIFS/etc..
$IPTABLES -A INPUT -p tcp -m multiport --dports 135,137,138,139,445,1433,1434 -j DROP
$IPTABLES -A INPUT -p udp -m multiport --dports 135,137,138,139,445,1433,1434 -j DROP
# Explicitly drop invalid incoming traffic
$IPTABLES -A INPUT -m state --state INVALID -j DROP
# Drop invalid outgoing traffic, too.
$IPTABLES -A OUTPUT -m state --state INVALID -j DROP
# If we would use NAT, INVALID packets would pass - BLOCK them anyways
$IPTABLES -A FORWARD -m state --state INVALID -j DROP
# PORT Scanners (stealth also)
$IPTABLES -A INPUT -m state --state NEW -p tcp --tcp-flags ALL ALL -j DROP
$IPTABLES -A INPUT -m state --state NEW -p tcp --tcp-flags ALL NONE -j DROP
# Some anti-spoofing rules
$IPTABLES -N SYN_FLOOD
$IPTABLES -A INPUT -p tcp --syn -j SYN_FLOOD
$IPTABLES -A SYN_FLOOD -m limit --limit 2/s --limit-burst 6 -j RETURN
$IPTABLES -A SYN_FLOOD -j DROP
# Allow outgoing DNS requests. Few things will work without this.
$IPTABLES -A OUTPUT -m state --state NEW -p udp --dport 53 -j ACCEPT
$IPTABLES -A OUTPUT -m state --state NEW -p tcp --dport 53 -j ACCEPT
# Allow outgoing HTTP requests. Unencrypted, use with care.
$IPTABLES -A OUTPUT -m state --state NEW -p tcp --dport 80 -j ACCEPT
# Allow outgoing HTTPS requests.
$IPTABLES -A OUTPUT -m state --state NEW -p tcp --dport 443 -j ACCEPT
# Allow outgoing SMTPS requests. Do NOT allow unencrypted SMTP!
# $IPTABLES -A OUTPUT -m state --state NEW -p tcp --dport 465 -j ACCEPT
# Allow outgoing "submission" (RFC 2476) requests.
$IPTABLES -A OUTPUT -m state --state NEW -p tcp --dport 587 -j ACCEPT
# Allow outgoing SSH requests.
$IPTABLES -A OUTPUT -m state --state NEW -p tcp --dport 22 -j ACCEPT
# Allow outgoing FTP requests. Unencrypted, use with care.
$IPTABLES -A OUTPUT -m state --state NEW -p tcp --dport 21 -j ACCEPT
# Allow outgoing MySQL requests. Unencrypted, use with care.
$IPTABLES -A OUTPUT -m state --state NEW -p tcp --dport 3306 -j ACCEPT
# Allow incoming DNS requests.
$IPTABLES -A INPUT -m state --state NEW -p udp --dport 53 -j ACCEPT
$IPTABLES -A INPUT -m state --state NEW -p tcp --dport 53 -j ACCEPT
# Allow incoming HTTP requests.
$IPTABLES -A INPUT -m state --state NEW -p tcp --dport 80 -j ACCEPT
# Allow incoming HTTPS requests.
$IPTABLES -A INPUT -m state --state NEW -p tcp --dport 443 -j ACCEPT
# Allow incoming SMTP requests.
$IPTABLES -A INPUT -m state --state NEW -p tcp --dport 25 -j ACCEPT
# Allow incoming SSH requests.
$IPTABLES -A INPUT -m state --state NEW -p tcp --dport 22 -j ACCEPT
# Allow incoming FTP requests.
$IPTABLES -A INPUT -m state --state NEW -p tcp --dport 21 -j ACCEPT
# Allow incoming MySQL requests.
$IPTABLES -A INPUT -m state --state NEW -p tcp --dport 3306 -j ACCEPT
# Explicitly log and reject everything else.
#------------------------------------------------------------------------------
# Use REJECT instead of REJECTLOG if you don't need/want logging.
$IPTABLES -A INPUT -j REJECTLOG
$IPTABLES -A OUTPUT -j REJECTLOG
$IPTABLES -A FORWARD -j REJECTLOG
exit 0
