Packet filtering setup script

Packet filtering setup script by Anthony C. Zboralski. Adapted by Didi Damian for iptables version 1.0.0

Sample:

PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# Set up variables
EXT_IF="eth0"
INT_IF="eth1"
EXT_IP=24.x.x.x/32
INT_IP=192.168.0.1/32
EXT_NET=24.x.x.0/24
INT_NET=192.168.0.0/24
MASQ_NETS="192.168.0.0/24"
LOCAL_ADDRS="127.0.0.0/8 192.168.0.1/32 24.x.x.x/32"
MAIL_RELAY=24.x.x.x/32
SMB_ACCESS="192.168.0.2/32"
SMB_BCAST="192.168.0.255/32"

# Turn on IP forwarding
echo Turning on IP forwarding.
echo 1 > /proc/sys/net/ipv4/ip_forward

# Load the ip_tables module
echo Loading ip_tables module.
/sbin/modprobe ip_tables || exit 1
# I let the kernel dynamically load the other modules

echo Flush standard tables.
iptables --flush INPUT
iptables --flush OUTPUT
iptables --flush FORWARD
echo Deny everything until firewall setup is completed.
iptables --policy INPUT DROP
iptables --policy OUTPUT DROP
iptables --policy FORWARD DROP

CHAINS=`iptables -n -L |perl -n -e /Chains+(S+)/ && !($1 =~ /^(INPUT|FORWARD|OUTPUT)$/) && print "$1 "`
echo Remove remaining chains:
echo $CHAINS
for chain in $CHAINS; do
iptables --flush $chain
done
# 2nd step cause of dependencies
for chain in $CHAINS; do
iptables --delete-chain $chain
done

for net in $MASQ_NETS; do
# I delete all the rules so you can rerun the scripts without bloating
# your nat entries.
iptables -D POSTROUTING -t nat -s $MASQ_NETS -j MASQUERADE 2>/dev/null
iptables -A POSTROUTING -t nat -s $MASQ_NETS -j MASQUERADE || exit 1
done
iptables --policy FORWARD ACCEPT

# Create a target for logging and dropping packets
iptables --new LDROP 2>/dev/null
iptables -A LDROP --proto tcp -j LOG --log-level info
--log-prefix "TCP Drop "
iptables -A LDROP --proto udp -j LOG --log-level info
--log-prefix "UDP Drop "
iptables -A LDROP --proto icmp -j LOG --log-level info
--log-prefix "ICMP Drop "
iptables -A LDROP --proto gre -j LOG --log-level info
--log-prefix "GRE Drop "

iptables -A LDROP -f -j LOG --log-level emerg
--log-prefix "FRAG Drop "
iptables -A LDROP -j DROP

# Create a table for watching some accepting rules
iptables --new WATCH 2>/dev/null
iptables -A WATCH -m limit -j LOG --log-level warn --log-prefix "ACCEPT "
iptables -A WATCH -j ACCEPT


echo Special target for local addresses:
iptables --new LOCAL 2>/dev/null
echo $LOCAL_ADDRS
for ip in $LOCAL_ADDRS; do
iptables -A INPUT --dst $ip -j LOCAL
# iptables -A INPUT --src $ip -i ! lo -j LDROP # lame spoof protect
done
echo Authorize mail from mail relay.
iptables -A LOCAL --proto tcp --syn --src $MAIL_RELAY --dst $EXT_IP --dport 25 -j ACCEPT


echo Authorizing samba access to:
echo $SMB_ACCESS
iptables --new SMB 2>/dev/null
for ip in $SMB_ACCESS; do
iptables -A SMB -s $ip -j ACCEPT
done
iptables -A LOCAL --proto udp -i ! $EXT_IF --dport 135:139 -j SMB
iptables -A LOCAL --proto tcp -i ! $EXT_IF --dport 135:139 -j SMB
iptables -A LOCAL --proto tcp -i ! $EXT_IF --dport 445 -j SMB
iptables -A INPUT -i ! $EXT_IF --dst $SMB_BCAST -j ACCEPT #lame samba broadcast

echo Drop and log every other incoming tcp connection attempts.
iptables -A LOCAL -i ! lo --proto tcp --syn --j LDROP

echo Authorize dns access for local nets.
for net in $MASQ_NETS 127.0.0.0/8; do
iptables -A INPUT --proto udp --src $net --dport 53 -j ACCEPT
done


echo Enforcing up ICMP policies, use iptables -L ICMP to check.
# If you deny all ICMP messages you head for trouble since it would
# break lots of tcp/ip algorythm (acz)
iptables --new ICMP 2>/dev/null
iptables -A INPUT --proto icmp -j ICMP
iptables -A ICMP -p icmp --icmp-type echo-reply -j ACCEPT
iptables -A ICMP -p icmp --icmp-type destination-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type network-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type host-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type protocol-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type port-unreachable -j ACCEPT
iptables -A ICMP -p icmp --icmp-type fragmentation-needed -j LDROP
iptables -A ICMP -p icmp --icmp-type source-route-failed -j WATCH
iptables -A ICMP -p icmp --icmp-type network-unknown -j WATCH
iptables -A ICMP -p icmp --icmp-type host-unknown -j WATCH
iptables -A ICMP -p icmp --icmp-type network-prohibited -j WATCH
iptables -A ICMP -p icmp --icmp-type host-prohibited -j WATCH
iptables -A ICMP -p icmp --icmp-type TOS-network-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type TOS-host-unreachable -j WATCH
iptables -A ICMP -p icmp --icmp-type communication-prohibited -j WATCH
iptables -A ICMP -p icmp --icmp-type host-precedence-violation -j LDROP
iptables -A ICMP -p icmp --icmp-type precedence-cutoff -j LDROP
iptables -A ICMP -p icmp --icmp-type source-quench -j LDROP
iptables -A ICMP -p icmp --icmp-type redirect -j LDROP
iptables -A ICMP -p icmp --icmp-type network-redirect -j LDROP
iptables -A ICMP -p icmp --icmp-type host-redirect -j LDROP
iptables -A ICMP -p icmp --icmp-type TOS-network-redirect -j LDROP
iptables -A ICMP -p icmp --icmp-type TOS-host-redirect -j LDROP
iptables -A ICMP -p icmp --icmp-type echo-request -j WATCH
iptables -A ICMP -p icmp --icmp-type router-advertisement -j LDROP
iptables -A ICMP -p icmp --icmp-type router-solicitation -j LDROP
iptables -A ICMP -p icmp --icmp-type time-exceeded -j WATCH
iptables -A ICMP -p icmp --icmp-type ttl-zero-during-transit -j WATCH
iptables -A ICMP -p icmp --icmp-type ttl-zero-during-reassembly -j WATCH
iptables -A ICMP -p icmp --icmp-type parameter-problem -j WATCH
iptables -A ICMP -p icmp --icmp-type ip-header-bad -j WATCH
iptables -A ICMP -p icmp --icmp-type required-option-missing -j WATCH
iptables -A ICMP -p icmp --icmp-type timestamp-request -j LDROP
iptables -A ICMP -p icmp --icmp-type timestamp-reply -j LDROP
iptables -A ICMP -p icmp --icmp-type address-mask-request -j LDROP
iptables -A ICMP -p icmp --icmp-type address-mask-reply -j LDROP
iptables -A ICMP -p icmp -j LDROP

echo Authorize tcp traffic.
iptables -A INPUT --proto tcp -j ACCEPT

echo Authorize packet output.
iptables --policy OUTPUT ACCEPT

#echo reject ident if you drop em you gotta wait for timeout
#iptables -I LOCAL --proto tcp --syn --dst $EXT_IP --dport 113 -j REJECT

echo Drop and log all udp below 1024.
iptables -A INPUT -i ! lo --proto udp --dport :1023 -j LDROP

echo Drop rpc dynamic udp port:
RPC_UDP=`rpcinfo -p localhost|perl -n -e /.*udps+(d+)s+/ && print $1,"n"|sort -u`
echo $RPC_UDP
for port in $RPC_UDP; do
iptables -A LOCAL -i ! lo --proto udp --dport $port -j LDROP
done

echo Authorize udp above 1024.
iptables -A INPUT --proto udp --dport 1024: -j ACCEPT