#!/bin/sh
# rc.fwsoho: SOHO IP Tables rule set
# Copyright 2003 Bob Toxen.  All rights reserved.
# See book "Real World Linux Security 2nd ed" for terms of use

#uncomment to see each line as it is executed
#set -v

# External interface
EXTIF=eth0
# Internal interface
INTIF=eth1

IPT=iptables
IFC=ifconfig
G=grep
SED=sed

$IPT        -P INPUT       DROP
$IPT        -P OUTPUT      DROP
$IPT        -P FORWARD     DROP
$IPT        -F

$IPT -t nat -P PREROUTING  DROP
$IPT -t nat -P POSTROUTING DROP
$IPT -t nat -P OUTPUT      DROP
$IPT -t nat -F

# dhclient (DHCP client) uses a raw socket that
# bypasses IP Tables.  Thus, it works even if all
# packets are blocked.  If you use a different program
# for DHCP to set the dynamic IP address of your
# Internet interface, the following may be uncommented:
# $IPT -I INPUT  -p UDP --sport 67 --dport 68 -j ACCEPT
# $IPT -I OUTPUT -p UDP --sport 68 --dport 67 -j ACCEPT

echo 1 > /proc/sys/net/ipv4/tcp_syncookies
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

# Source Address Verification
for f in /proc/sys/net/ipv4/conf/*/rp_filter; do
        echo 1 > $f
done
# Disable IP source routing and ICMP redirects
for f in /proc/sys/net/ipv4/conf/*/accept_source_route; do
        echo 0 > $f
done
for f in /proc/sys/net/ipv4/conf/*/accept_redirects; do
        echo 0 > $f
done

echo 1 > /proc/sys/net/ipv4/ip_forward

EXTIP="`$IFC $EXTIF|$G addr:|$SED 's/.*addr:\([^ ]*\) .*/\1/'`"
EXTBC="`$IFC $EXTIF|$G Bcast:|$SED 's/.*Bcast:\([^ ]*\) .*/\1/'`"
EXTMSK="`$IFC $EXTIF|$G Mask:|$SED 's/.*Mask:\([^ ]*\)/\1/'`"
EXTNET="$EXTIP/$EXTMSK"
echo "EXTIP=$EXTIP EXTBC=$EXTBC EXTMSK=$EXTMSK EXTNET=$EXTNET"

INTIP="`$IFC $INTIF|$G addr:|$SED 's/.*addr:\([^ ]*\) .*/\1/'`"
INTBC="`$IFC $INTIF|$G Bcast:|$SED 's/.*Bcast:\([^ ]*\) .*/\1/'`"
INTMSK="`$IFC $INTIF|$G Mask:|$SED 's/.*Mask:\([^ ]*\)/\1/'`"
INTNET="$INTIP/$INTMSK"
echo "INTIP=$INTIP INTBC=$INTBC INTMSK=$INTMSK INTNET=$INTNET"

LPDIF=lo
LPDIP=127.0.0.1
LPDMSK=255.0.0.0
LPDNET="$LPDIP/$LPDMSK"

# Do not complain if chain already exists (so restart is clean)
$IPT -N DROPl   2> /dev/null
$IPT -A DROPl   -j LOG --log-prefix 'DROPl:'
$IPT -A DROPl   -j DROP

$IPT -N REJECTl 2> /dev/null
$IPT -A REJECTl -j LOG --log-prefix 'REJECTl:'
$IPT -A REJECTl -j REJECT

$IPT -A INPUT   -i $LPDIF -s   $LPDIP  -j ACCEPT
$IPT -A INPUT   -i $LPDIF -s   $EXTIP  -j ACCEPT
$IPT -A INPUT   -i $LPDIF -s   $INTIP  -j ACCEPT

# Block broadcasts
# (We could also do -s rules)
$IPT -A INPUT   -i $EXTIF -d   $EXTBC  -j DROPl
$IPT -A INPUT   -i $INTIF -d   $INTBC  -j DROPl
$IPT -A OUTPUT  -o $EXTIF -d   $EXTBC  -j DROPl
$IPT -A OUTPUT  -o $INTIF -d   $INTBC  -j DROPl
$IPT -A FORWARD -o $EXTIF -d   $EXTBC  -j DROPl
$IPT -A FORWARD -o $INTIF -d   $INTBC  -j DROPl

# Block Internet from trying to access internal or route thru us
$IPT -A INPUT   -i $EXTIF -d ! $EXTIP  -j DROPl

# Block internal with bad network address
$IPT -A INPUT   -i $INTIF -s ! $INTNET -j DROPl
$IPT -A OUTPUT  -o $INTIF -d ! $INTNET -j DROPl
$IPT -A FORWARD -i $INTIF -s ! $INTNET -j DROPl
$IPT -A FORWARD -o $INTIF -d ! $INTNET -j DROPl

# One last Egress check for sanity
$IPT -A OUTPUT  -o $EXTIF -s ! $EXTNET -j DROPl

# Block outbound ICMP (except ping)
$IPT -A OUTPUT  -o $EXTIF -p icmp \
  --icmp-type ! 8 -j DROPl
$IPT -A FORWARD -o $EXTIF -p icmp \
  --icmp-type ! 8 -j DROPl

. /etc/rc.d/fw.trouble

# Frequently attacked blocked services: COM blocks both TCP&UDP, TCP, UDP
# Note that ALL UDP ports can be abused by attackers to have YOU do
#   a DoS attack against the third party of their choice; this is why
#   even benign UDP services are blocked
# TCP 53 is listed separately since some sites do Zone Transfers between systems

# COMmon ports:
# 0 is tcpmux; SGI had vulnerability, 1 is common attack
# 13 is daytime
# 98 is Linuxconf
# 111 is sunrpc (portmap)
# 137:139, 445 is Microsoft
# 161:162 is SNMP
# Squid flotilla: 3128, 8000, 8008, 8080
# 1214 is Morpheus or KaZaA
# 2049 is NFS
# 3049 is very virulent Linux Trojan, mistakable for NFS
# Common attacks: 1999, 4329, 6346
# Common Trojans 12345 65535
COMBLOCK="0:1 13 98 111 137:139 161:162 445 1214 1999 2049 3049 4329 6346 3128 8000 8008 8080 12345 65535"

# TCP ports:
# 512-515 is rexec, rlogin, rsh, printer(lpd)
#   [very serious vulnerabilities; attacks continue daily]
# 1080 is Socks proxy server
# 6000 is X (NOTE X over SSH is secure and runs on TCP 22)
# Block 6112 (Sun's/HP's CDE)
TCPBLOCK="$COMBLOCK 512:515 1080 6000:6009 6112"

# UDP ports:
# 520=RIP, 9000 is Sangoma
# 517:518 are talk and ntalk (more annoying than anything)
UDPBLOCK="$COMBLOCK 520 517:518 1427 9000"

echo -n "FW: Blocking attacks to TCP port "
for i in $TCPBLOCK;
do
  echo -n "$i "
  $IPT -A INPUT   -p tcp --dport $i  -j DROPl
  $IPT -A OUTPUT  -p tcp --dport $i  -j DROPl
  $IPT -A FORWARD -p tcp --dport $i  -j DROPl
done
echo ""

echo -n "FW: Blocking attacks to UDP port "
for i in $UDPBLOCK;
do
  echo -n "$i "
  $IPT -A INPUT   -p udp --dport $i  -j DROPl
  $IPT -A OUTPUT  -p udp --dport $i  -j DROPl
  $IPT -A FORWARD -p udp --dport $i  -j DROPl
done
echo ""

MODULES="ip_nat_ftp ip_conntrack_ftp"
for i in $MODULES;
do
  echo "Inserting module $i"
  modprobe $i
done

TCPSERV="domain ssh http https ftp ftp-data mail pop3 pop3s imap3 imaps 11371 time"
UDPSERV="domain time ntp"
echo -n "FW: Allowing inside systems to use service:"
for i in $TCPSERV;
do
  echo -n "$i "
  $IPT -A OUTPUT  -o $EXTIF -p tcp -s $EXTIP  \
    --dport $i --syn -m state --state NEW -j ACCEPT
  $IPT -A FORWARD -i $INTIF -p tcp -s $INTNET \
    --dport $i --syn -m state --state NEW -j ACCEPT
done
echo ""

echo -n "FW: Allowing inside systems to use service:"
for i in $UDPSERV;
do
  echo -n "$i "
  $IPT -A OUTPUT  -o $EXTIF -p udp -s $EXTIP  \
    --dport $i -m state --state NEW -j ACCEPT
  $IPT -A FORWARD -i $INTIF -p udp -s $INTNET \
    --dport $i -m state --state NEW -j ACCEPT
done
echo ""

# Allow to ping out
$IPT -A OUTPUT  -o $EXTIF -p icmp -s $EXTIP  \
  --icmp-type 8 -m state --state NEW -j ACCEPT
$IPT -A FORWARD -i $INTIF -p icmp -s $INTNET \
  --icmp-type 8 -m state --state NEW -j ACCEPT

# Allow firewall to ping internal systems
$IPT -A OUTPUT  -o $INTIF -p icmp -s $INTNET \
  --icmp-type 8 -m state --state NEW -j ACCEPT

# $IPT -A INPUT   -i $EXTIF -p tcp --dport 22 \
#   --syn -m state --state NEW -j ACCEPT

# $IPT -A INPUT   -i $EXTIF -p tcp -s pentacorp.com/24  --dport 22 \
#   --syn -m state --state NEW -j ACCEPT
# $IPT -A INPUT   -i $EXTIF -p tcp -s chemwiz.state.edu --dport 22 \
#   --syn -m state --state NEW -j ACCEPT

# Connect only from hardened systems
# (hopefully only those running Linux or Unix hardened as per the book)
# $IPT -A INPUT   -i $INTIF -p tcp                      --dport 22 \
#   --syn -m state --state NEW -j ACCEPT

# Connect only to hardened systems
# (hopefully only those running Linux or Unix hardened as per the book)
# $IPT -A OUTPUT  -o $INTIF -p tcp                      --dport 22 \
#   -d 10.0.0.42 --syn -m state --state NEW -j ACCEPT

$IPT -t nat -A PREROUTING                       -j ACCEPT
# $IPT -t nat -A POSTROUTING -o $EXTIF -s $INTNET -j SNAT --to $EXTIP
# Comment out next line (that has "MASQUERADE") to not NAT internal network
$IPT -t nat -A POSTROUTING -o $EXTIF -s $INTNET -j MASQUERADE
$IPT -t nat -A POSTROUTING                      -j ACCEPT
$IPT -t nat -A OUTPUT                           -j ACCEPT

$IPT -A INPUT   -p tcp --dport auth --syn -m state --state NEW -j ACCEPT

iptables -A INPUT   -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A OUTPUT  -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT

# Log & block whatever is left
$IPT -A INPUT             -j DROPl
$IPT -A OUTPUT            -j REJECTl
$IPT -A FORWARD           -j DROPl