firewall.sh

#!/bin/sh
# MIS Firewall Script v1.0
#
# Author: gabe@mudbuginfo.com
#         Based on O'reilly Linux Server Hacks, #45
#
# Documentation forthcoming
# This script must be run after a boot, as iptables does not save its state
#
#< I. Configuration Options >###################################################

WHITELIST=/etc/firewall.whitelist
BLACKLIST=/etc/firewall.blacklist

# List of PUBLICALLY allowed ports, delimited by spaces
PUBLIC_TCP_PORTS="20 21 22 53 80 443 2575 30000:30050"
PUBLIC_UDP_PORTS="53"

SYN_LIMIT="600/s"
SYN_LIMIT_BURST="800"
LOG_LIMIT="2/s"
LOG_LIMIT_BURST="10"

#< II. Program Locations >######################################################

AWK=/usr/bin/awk
ECHO=echo
GREP=/bin/grep
ID=/usr/bin/id
IPTABLES=/sbin/iptables
SORT=/usr/bin/sort
UNIQ=/usr/bin/uniq

if [ ! -z $DEBUG ]; then
IPTABLES="debug $IPTABLES"
fi

#< III. Functions >#############################################################

function error() {
	$ECHO "$0: $@" 1>&2
	$EXIT 1
}

function debug() {
	if [ ! -z $DEBUG ]; then
		$ECHO "$0 DEBUG: $@" 1>&2
	fi
}


#< IV. Sanitize >###############################################################

if [ `$ID -u` != 0 ]; then error "must be root user to execute, exiting..."; fi;
if [ ! -e "$WHITELIST" ]; then error "WHITELIST $WHITELIST does not exist"; fi;
if [ ! -e "$BLACKLIST" ]; then error "BLACKLIST $BLACKLIST does not exist"; fi;


#< V. Firewall Script Body >####################################################

$ECHO "--- Setting up sysctl options"
$ECHO "1" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
$ECHO "0" > /proc/sys/net/ipv4/tcp_timestamps
# Doesn't exist in 2.6.  Re-examine at my leisure
#$ECHO "1" > /proc/sys/net/ipv4/tcp_syncookies
$ECHO "1" > /proc/sys/net/ipv4/conf/all/log_martians
for i in /proc/sys/net/ipv4/conf/*/rp_filter; do
	$ECHO "1" > $i
done



# Clear all current rules, its only proper
$IPTABLES -F
$IPTABLES -X



echo "--- Adding Whitelist"
# Process the white list
$IPTABLES -N WHITELIST
for i in `$GREP -v \^# $WHITELIST | $AWK '{print $1}' | $SORT | $UNIQ`; do
	debug "Allowing $i"
	$IPTABLES -A WHITELIST -t filter --source $i -j ACCEPT
done


echo "--- Adding Blacklist (LOGGED)"
# Process the black list
$IPTABLES -N BLACKLIST_LOG
$IPTABLES -A BLACKLIST_LOG -j LOG --log-prefix "fp=BLACKLIST a=DROP "
$IPTABLES -A BLACKLIST_LOG -j DROP
$IPTABLES -N BLACKLIST
for i in `$GREP -v \^# $BLACKLIST | $AWK '{print $1}' | $SORT | $UNIQ`; do
	debug "Blocking $i"
	#$IPTABLES -A BLACKLIST -t filter --source $i -j BLACKLIST_LOG
	$IPTABLES -A BLACKLIST -t filter --source $i -j DROP
done


echo "--- Checking for Bad TCP Flags (LOGGED)"
$IPTABLES -N MALICIOUS_FLAGS_LOG
$IPTABLES -A MALICIOUS_FLAGS_LOG -m limit --limit $LOG_LIMIT --limit-burst $LOG_LIMIT_BURST -j LOG --log-prefix "chain=MALICIOUS_FLAGS a=DROP "
$IPTABLES -A MALICIOUS_FLAGS_LOG -j DROP
$IPTABLES -N MALICIOUS_FLAGS
$IPTABLES -A MALICIOUS_FLAGS -p tcp --tcp-flags ALL FIN,URG,PSH -j MALICIOUS_FLAGS_LOG
$IPTABLES -A MALICIOUS_FLAGS -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j MALICIOUS_FLAGS_LOG
$IPTABLES -A MALICIOUS_FLAGS -p tcp --tcp-flags ALL ALL -j MALICIOUS_FLAGS_LOG
$IPTABLES -A MALICIOUS_FLAGS -p tcp --tcp-flags ALL NONE -j MALICIOUS_FLAGS_LOG
$IPTABLES -A MALICIOUS_FLAGS -p tcp --tcp-flags SYN,RST SYN,RST -j MALICIOUS_FLAGS_LOG
$IPTABLES -A MALICIOUS_FLAGS -p tcp --tcp-flags SYN,FIN SYN,FIN -j MALICIOUS_FLAGS_LOG



echo "--- Blocking 'Backdoor' ports (LOGGED)"
$IPTABLES -N MALICIOUS_PORTS_LOG
$IPTABLES -A MALICIOUS_PORTS_LOG -m limit --limit $LOG_LIMIT --limit-burst $LOG_LIMIT_BURST -j LOG --log-prefix "chain=MALICIOUS_PORTS a=DROP "
$IPTABLES -A MALICIOUS_PORTS_LOG -j DROP
$IPTABLES -N MALICIOUS_PORTS
# Deepthroat
$IPTABLES -A MALICIOUS_PORTS -p tcp --dport 6670 -j MALICIOUS_PORTS_LOG
# Subseven
$IPTABLES -A MALICIOUS_PORTS -p tcp --dport 1243 -j MALICIOUS_PORTS_LOG
$IPTABLES -A MALICIOUS_PORTS -p udp --dport 1243 -j MALICIOUS_PORTS_LOG
$IPTABLES -A MALICIOUS_PORTS -p tcp --dport 27374 -j MALICIOUS_PORTS_LOG
$IPTABLES -A MALICIOUS_PORTS -p udp --dport 27374 -j MALICIOUS_PORTS_LOG
$IPTABLES -A MALICIOUS_PORTS -p tcp --dport 6711:6713 -j MALICIOUS_PORTS_LOG
# Netbus
$IPTABLES -A MALICIOUS_PORTS -p tcp --dport 12345:12346 -j MALICIOUS_PORTS_LOG
$IPTABLES -A MALICIOUS_PORTS -p tcp --dport 20034 -j MALICIOUS_PORTS_LOG
# Back Orifice
$IPTABLES -A MALICIOUS_PORTS -p tcp --dport 31337:31338 -j MALICIOUS_PORTS_LOG
# Hack'a'Tack 2000
$IPTABLES -A MALICIOUS_PORTS -p tcp --dport 28431 -j MALICIOUS_PORTS_LOG



#echo "--- Blocking SYN floods (LOGGED)"
#$IPTABLES -N SYNFLOOD_LOG
#$IPTABLES -A SYNFLOOD_LOG -m limit --limit $LOG_LIMIT --limit-burst $LOG_LIMIT_BURST -j LOG --log-prefix "chain=SYN_FLOOD a=DROP "
#$IPTABLES -A SYNFLOOD_LOG -j DROP
$IPTABLES -N TCP_ACCEPT
$IPTABLES -A TCP_ACCEPT -p tcp -j ACCEPT # The syn flood blocking is being *too* proactive. blocking them for now.
#$IPTABLES -A TCP_ACCEPT -p tcp --syn -m limit --limit $SYN_LIMIT --limit-burst $SYN_LIMIT_BURST -j ACCEPT
#$IPTABLES -A TCP_ACCEPT -p tcp --syn -j SYNFLOOD_LOG
#$IPTABLES -A TCP_ACCEPT -p tcp ! --syn -j ACCEPT


echo "--- Allowing TCP Services: $PUBLIC_TCP_PORTS"
$IPTABLES -N TCP_SERVICES
for i in $PUBLIC_TCP_PORTS; do
	debug "Allowing public access of tcp port $i"
	$IPTABLES -A TCP_SERVICES -t filter -p tcp --destination-port $i -j TCP_ACCEPT
done

echo "--- Allowing UDP Services: $PUBLIC_UDP_PORTS"
$IPTABLES -N UDP_SERVICES
for i in $PUBLIC_UDP_PORTS; do
	debug "Allowing public access of udp port $i"
	$IPTABLES -A UDP_SERVICES -t filter -p udp --destination-port $i -j ACCEPT
done




#
# This is the INPUT chain "money shot"
#
$IPTABLES -A INPUT -j WHITELIST
$IPTABLES -A INPUT -j BLACKLIST
$IPTABLES -A INPUT -p tcp -j MALICIOUS_FLAGS
$IPTABLES -A INPUT -j MALICIOUS_PORTS
$IPTABLES -A INPUT -p tcp -j TCP_SERVICES
$IPTABLES -A INPUT -p udp -j UDP_SERVICES




# Special blocking for IDENT
echo "--- REJECTing Ident tcp/113 requests"
$IPTABLES -A INPUT -p tcp --dport 113 -j REJECT --reject-with tcp-reset

echo "--- DROPing all other new incoming connections"
# And block anything else that tries to connect
$IPTABLES -A INPUT -t filter -p tcp --syn -j DROP


################################################################################
#< Finished >###################################################################
################################################################< have a beer >#