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#!/bin/sh
#———
#
# File: SIG-antiDDoS.sh
#
# Configuration.
#———
  
# For debugging use iptables -v.
IPTABLES=”/sbin/iptables”
IP6TABLES=”/sbin/ip6tables”
MODPROBE=”/sbin/modprobe”
RMMOD=”/sbin/rmmod”
ARP=”/usr/sbin/arp”
  
# 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″

# Unprivileged ports.
#———
PHIGH=”1024:65535″
PSSH=”1000:1023″
  
# Load required kernel modules
#———
$MODPROBE ip_conntrack_ftp
$MODPROBE ip_conntrack_irc
  
# Mitigate ARP spoofing/poisoning and similar attacks.
#———
# Hardcode static ARP cache entries here
# $ARP -s IP-ADDRESS MAC-ADDRESS
  
# Kernel configuration.
#———
  
# Disable IP forwarding.
# On => Off = (reset)
echo 1 > /proc/sys/net/ipv4/ip_forward
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
  
# Disable multicast routing
for i in /proc/sys/net/ipv4/conf/*/mc_forwarding; do echo 0 > $i; done
  
# Disable proxy_arp.
for i in /proc/sys/net/ipv4/conf/*/proxy_arp; do echo 0 > $i; done
  
# Enable secure redirects, i.e. only accept ICMP redirects for gateways
# Helps against MITM attacks.
for i in /proc/sys/net/ipv4/conf/*/secure_redirects; do echo 1 > $i; done
  
# Disable bootp_relay
for i in /proc/sys/net/ipv4/conf/*/bootp_relay; do echo 0 > $i; done
  
# Default policies.
#———
  
# 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
  
# Cleanup.
#———
  
# 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
  
# Completely disable IPv6.
#———
  
# Block all IPv6 traffic
# If the ip6tables command is available, try to block all IPv6 traffic.
if test -x $IP6TABLES; then
# Set the default policies
# drop everything
$IP6TABLES -P INPUT DROP 2>/dev/null
$IP6TABLES -P FORWARD DROP 2>/dev/null
$IP6TABLES -P OUTPUT DROP 2>/dev/null
  
# The mangle table can pass everything
$IP6TABLES -t mangle -P PREROUTING ACCEPT 2>/dev/null
$IP6TABLES -t mangle -P INPUT ACCEPT 2>/dev/null
$IP6TABLES -t mangle -P FORWARD ACCEPT 2>/dev/null
$IP6TABLES -t mangle -P OUTPUT ACCEPT 2>/dev/null
$IP6TABLES -t mangle -P POSTROUTING ACCEPT 2>/dev/null
  
# Delete all rules.
$IP6TABLES -F 2>/dev/null
$IP6TABLES -t mangle -F 2>/dev/null
  
# Delete all chains.
$IP6TABLES -X 2>/dev/null
$IP6TABLES -t mangle -X 2>/dev/null
  
# Zero all packets and counters.
$IP6TABLES -Z 2>/dev/null
$IP6TABLES -t mangle -Z 2>/dev/null
fi
  
# Custom user-defined chains.
#———
  
# 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
  
# Only allows RELATED ICMP types
# (destination-unreachable, time-exceeded, and parameter-problem).
# TODO: Rate-limit this traffic?
# TODO: Allow fragmentation-needed?
# TODO: Test.
$IPTABLES -N RELATED_ICMP
$IPTABLES -A RELATED_ICMP -p icmp –icmp-type destination-unreachable -j ACCEPT
$IPTABLES -A RELATED_ICMP -p icmp –icmp-type time-exceeded -j ACCEPT
$IPTABLES -A RELATED_ICMP -p icmp –icmp-type parameter-problem -j ACCEPT
$IPTABLES -A RELATED_ICMP -j DROPLOG
  
# 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
  
# Only allow the minimally required/recommended parts of ICMP. Block the rest.
#———
  
# TODO: This section needs a lot of testing!
  
# 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
  
# Selectively allow certain special types of traffic.
#———
  
# 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
  
# Miscellaneous.
#———
  
# 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
  
# TODO: Some more anti-spoofing rules? For example:
# $IPTABLES -A INPUT -p tcp –tcp-flags ALL FIN,URG,PSH -j DROP
# $IPTABLES -A INPUT -p tcp –tcp-flags SYN,RST SYN,RST -j DROP
# $IPTABLES -A INPUT -p tcp –tcp-flags SYN,FIN SYN,FIN -j DROP
$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
  
# TODO: Block known-bad IPs
# $IPTABLES -A INPUT -s INSERT-BAD-IP-HERE -j DROPLOG
  
# Drop any traffic from IANA-reserved IPs.
#———
  
$IPTABLES -A INPUT -s 0.0.0.0/7 -j DROP
$IPTABLES -A INPUT -s 2.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 5.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 7.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 10.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 23.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 27.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 31.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 36.0.0.0/7 -j DROP
$IPTABLES -A INPUT -s 39.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 42.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 49.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 50.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 77.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 78.0.0.0/7 -j DROP
$IPTABLES -A INPUT -s 92.0.0.0/6 -j DROP
$IPTABLES -A INPUT -s 96.0.0.0/4 -j DROP
$IPTABLES -A INPUT -s 112.0.0.0/5 -j DROP
$IPTABLES -A INPUT -s 120.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 169.254.0.0/16 -j DROP
$IPTABLES -A INPUT -s 172.16.0.0/12 -j DROP
$IPTABLES -A INPUT -s 173.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 174.0.0.0/7 -j DROP
$IPTABLES -A INPUT -s 176.0.0.0/5 -j DROP
$IPTABLES -A INPUT -s 184.0.0.0/6 -j DROP
$IPTABLES -A INPUT -s 192.0.2.0/24 -j DROP
$IPTABLES -A INPUT -s 197.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 198.18.0.0/15 -j DROP
$IPTABLES -A INPUT -s 223.0.0.0/8 -j DROP
$IPTABLES -A INPUT -s 224.0.0.0/3 -j DROP
  
# Selectively allow certain outbound connections, block the rest.
#———
  
# 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 POP3S requests.
$IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 995 -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 NNTP requests. Unencrypted, use with care.
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 119 -j ACCEPT
  
# Allow outgoing NTP requests. Unencrypted, use with care.
# $IPTABLES -A OUTPUT -m state –state NEW -p udp –dport 123 -j ACCEPT
  
# Allow outgoing IRC requests. Unencrypted, use with care.
# Note: This usually needs the ip_conntrack_irc kernel module.
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 6667 -j ACCEPT
  
# Allow outgoing requests to various proxies. Unencrypted, use with care.
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 8080 -j ACCEPT
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 8090 -j ACCEPT
  
# Allow outgoing DHCP requests. Unencrypted, use with care.
# TODO: This is completely untested, I have no idea whether it works!
# TODO: I think this can be tightened a bit more.
$IPTABLES -A OUTPUT -m state –state NEW -p udp –sport 67:68 –dport 67:68 -j ACCEPT
  
# Allow outgoing CVS requests. Unencrypted, use with care.
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 2401 -j ACCEPT
  
# Allow outgoing MySQL requests. Unencrypted, use with care.
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 3306 -j ACCEPT
  
# Allow outgoing SVN requests. Unencrypted, use with care.
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 3690 -j ACCEPT
  
# Allow outgoing PLESK requests. Unencrypted, use with care.
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 8443 -j ACCEPT
  
# Allow outgoing Tor requests.
# Note: Do _not_ use unencrypted protocols over Tor (sniffing is possible)!
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 9001 -j ACCEPT
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 9002 -j ACCEPT
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 9030 -j ACCEPT
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 9031 -j ACCEPT
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 9090 -j ACCEPT
# $IPTABLES -A OUTPUT -m state –state NEW -p tcp –dport 9091 -j ACCEPT
  
# Allow outgoing OpenVPN requests.
$IPTABLES -A OUTPUT -m state –state NEW -p udp –dport 1194 -j ACCEPT
  
# TODO: ICQ, MSN, GTalk, Skype, Yahoo, etc…
  
# Selectively allow certain inbound connections, block the rest.
#———
  
# 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 POP3 requests.
$IPTABLES -A INPUT -m state –state NEW -p tcp –dport 110 -j ACCEPT
  
# Allow incoming IMAP4 requests.
$IPTABLES -A INPUT -m state –state NEW -p tcp –dport 143 -j ACCEPT
  
# Allow incoming POP3S requests.
$IPTABLES -A INPUT -m state –state NEW -p tcp –dport 995 -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 NNTP requests.
# $IPTABLES -A INPUT -m state –state NEW -p tcp –dport 119 -j ACCEPT
  
# Allow incoming MySQL requests.
# $IPTABLES -A INPUT -m state –state NEW -p tcp –dport 3306 -j ACCEPT
  
# Allow incoming PLESK requests.
# $IPTABLES -A INPUT -m state –state NEW -p tcp –dport 8843 -j ACCEPT
  
# Allow incoming BitTorrent requests.
# TODO: Are these already handled by ACCEPTing established/related traffic?
# $IPTABLES -A INPUT -m state –state NEW -p tcp –dport 6881 -j ACCEPT
# $IPTABLES -A INPUT -m state –state NEW -p udp –dport 6881 -j ACCEPT
  
# Allow incoming nc requests.
# $IPTABLES -A INPUT -m state –state NEW -p tcp –dport 2030 -j ACCEPT
# $IPTABLES -A INPUT -m state –state NEW -p udp –dport 2030 -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
  
#———
# Testing the firewall.
#———
  
# You should check/test that the firewall really works, using
# iptables -vnL, nmap, ping, telnet, …
  
# Exit gracefully.
#———
exit 0