#!/sbin/runscript # From http://www.gentoo.org/doc/en/security/security-handbook.xml?full=1#book_part1_chap12 IPTABLES=/sbin/iptables IPTABLESSAVE=/sbin/iptables-save IPTABLESRESTORE=/sbin/iptables-restore FIREWALL=/etc/firewall.rules DNS1=212.242.40.3 DNS2=212.242.40.51 #inside IIP=10.0.0.2 IINTERFACE=eth0 LOCAL_NETWORK=10.0.0.0/24 #outside OIP=217.157.156.144 OINTERFACE=eth1 opts="${opts} showstatus panic save restore showoptions rules" depend() { need net } rules() { stop ebegin "Setting internal rules" einfo "Setting default rule to drop" $IPTABLES -P FORWARD DROP $IPTABLES -P INPUT DROP $IPTABLES -P OUTPUT DROP #default rule einfo "Creating states chain" $IPTABLES -N allowed-connection $IPTABLES -F allowed-connection $IPTABLES -A allowed-connection -m state --state ESTABLISHED,RELATED -j ACCEPT $IPTABLES -A allowed-connection -i $IINTERFACE -m limit -j LOG --log-prefix \ "Bad packet from ${IINTERFACE}:" $IPTABLES -A allowed-connection -j DROP #ICMP traffic einfo "Creating icmp chain" $IPTABLES -N icmp_allowed $IPTABLES -F icmp_allowed $IPTABLES -A icmp_allowed -m state --state NEW -p icmp --icmp-type \ time-exceeded -j ACCEPT $IPTABLES -A icmp_allowed -m state --state NEW -p icmp --icmp-type \ destination-unreachable -j ACCEPT $IPTABLES -A icmp_allowed -p icmp -j LOG --log-prefix "Bad ICMP traffic:" $IPTABLES -A icmp_allowed -p icmp -j DROP #Incoming traffic einfo "Creating incoming ssh traffic chain" $IPTABLES -N allow-ssh-traffic-in $IPTABLES -F allow-ssh-traffic-in #Flood protection $IPTABLES -A allow-ssh-traffic-in -m limit --limit 1/second -p tcp --tcp-flags \ ALL RST --dport ssh -j ACCEPT $IPTABLES -A allow-ssh-traffic-in -m limit --limit 1/second -p tcp --tcp-flags \ ALL FIN --dport ssh -j ACCEPT $IPTABLES -A allow-ssh-traffic-in -m limit --limit 1/second -p tcp --tcp-flags \ ALL SYN --dport ssh -j ACCEPT $IPTABLES -A allow-ssh-traffic-in -m state --state RELATED,ESTABLISHED -p tcp --dport ssh -j ACCEPT #outgoing traffic einfo "Creating outgoing ssh traffic chain" $IPTABLES -N allow-ssh-traffic-out $IPTABLES -F allow-ssh-traffic-out $IPTABLES -A allow-ssh-traffic-out -p tcp --dport ssh -j ACCEPT einfo "Creating outgoing dns traffic chain" $IPTABLES -N allow-dns-traffic-out $IPTABLES -F allow-dns-traffic-out $IPTABLES -A allow-dns-traffic-out -p udp -d $DNS1 --dport domain \ -j ACCEPT $IPTABLES -A allow-dns-traffic-out -p udp -d $DNS2 --dport domain \ -j ACCEPT einfo "Creating outgoing http/https traffic chain" $IPTABLES -N allow-www-traffic-out $IPTABLES -F allow-www-traffic-out $IPTABLES -A allow-www-traffic-out -p tcp --dport www -j ACCEPT $IPTABLES -A allow-www-traffic-out -p tcp --dport https -j ACCEPT #Catch portscanners einfo "Creating portscan detection chain" $IPTABLES -N check-flags $IPTABLES -F check-flags $IPTABLES -A check-flags -p tcp --tcp-flags ALL FIN,URG,PSH -m limit \ --limit 5/minute -j LOG --log-level alert --log-prefix "NMAP-XMAS:" $IPTABLES -A check-flags -p tcp --tcp-flags ALL FIN,URG,PSH -j DROP $IPTABLES -A check-flags -p tcp --tcp-flags ALL ALL -m limit --limit \ 5/minute -j LOG --log-level 1 --log-prefix "XMAS:" $IPTABLES -A check-flags -p tcp --tcp-flags ALL ALL -j DROP $IPTABLES -A check-flags -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG \ -m limit --limit 5/minute -j LOG --log-level 1 --log-prefix "XMAS-PSH:" $IPTABLES -A check-flags -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP $IPTABLES -A check-flags -p tcp --tcp-flags ALL NONE -m limit \ --limit 5/minute -j LOG --log-level 1 --log-prefix "NULL_SCAN:" $IPTABLES -A check-flags -p tcp --tcp-flags ALL NONE -j DROP $IPTABLES -A check-flags -p tcp --tcp-flags SYN,RST SYN,RST -m limit \ --limit 5/minute -j LOG --log-level 5 --log-prefix "SYN/RST:" $IPTABLES -A check-flags -p tcp --tcp-flags SYN,RST SYN,RST -j DROP $IPTABLES -A check-flags -p tcp --tcp-flags SYN,FIN SYN,FIN -m limit \ --limit 5/minute -j LOG --log-level 5 --log-prefix "SYN/FIN:" $IPTABLES -A check-flags -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP # Apply and add invalid states to the chains einfo "Applying chains to INPUT" $IPTABLES -A INPUT -m state --state INVALID -j DROP $IPTABLES -A INPUT -j icmp_allowed $IPTABLES -A INPUT -j check-flags $IPTABLES -A INPUT -i lo -j ACCEPT $IPTABLES -A INPUT -j allow-ssh-traffic-in $IPTABLES -A INPUT -j allowed-connection einfo "Applying chains to FORWARD" $IPTABLES -A FORWARD -m state --state INVALID -j DROP $IPTABLES -A FORWARD -j icmp_allowed $IPTABLES -A FORWARD -j check-flags $IPTABLES -A FORWARD -o lo -j ACCEPT $IPTABLES -A FORWARD -j allow-ssh-traffic-in $IPTABLES -A FORWARD -j allow-www-traffic-out $IPTABLES -A FORWARD -j allowed-connection einfo "Applying chains to OUTPUT" $IPTABLES -A OUTPUT -m state --state INVALID -j DROP $IPTABLES -A OUTPUT -j icmp_allowed $IPTABLES -A OUTPUT -j check-flags $IPTABLES -A OUTPUT -o lo -j ACCEPT $IPTABLES -A OUTPUT -j allow-ssh-traffic-out $IPTABLES -A OUTPUT -j allow-dns-traffic-out $IPTABLES -A OUTPUT -j allow-www-traffic-out $IPTABLES -A OUTPUT -j allowed-connection #Allow client to route through via NAT (Network Address Translation) $IPTABLES -t nat -A POSTROUTING -o $IINTERFACE -j MASQUERADE eend $? } start() { ebegin "Starting firewall" if [ -e "${FIREWALL}" ]; then restore else einfo "${FIREWALL} does not exists. Using default rules." rules fi eend $? } stop() { ebegin "Stopping firewall" $IPTABLES -F $IPTABLES -t nat -F $IPTABLES -X $IPTABLES -P FORWARD ACCEPT $IPTABLES -P INPUT ACCEPT $IPTABLES -P OUTPUT ACCEPT eend $? } showstatus() { ebegin "Status" $IPTABLES -L -n -v --line-numbers einfo "NAT status" $IPTABLES -L -n -v --line-numbers -t nat eend $? } panic() { ebegin "Setting panic rules" $IPTABLES -F $IPTABLES -X $IPTABLES -t nat -F $IPTABLES -P FORWARD DROP $IPTABLES -P INPUT DROP $IPTABLES -P OUTPUT DROP $IPTABLES -A INPUT -i lo -j ACCEPT $IPTABLES -A OUTPUT -o lo -j ACCEPT eend $? } save() { ebegin "Saving Firewall rules" $IPTABLESSAVE > $FIREWALL eend $? } restore() { ebegin "Restoring Firewall rules" $IPTABLESRESTORE < $FIREWALL eend $? } restart() { svc_stop; svc_start } showoptions() { echo "Usage: $0 {start|save|restore|panic|stop|restart|showstatus}" echo "start) will restore setting if exists else force rules" echo "stop) delete all rules and set all to accept" echo "rules) force settings of new rules" echo "save) will store settings in ${FIREWALL}" echo "restore) will restore settings from ${FIREWALL}" echo "showstatus) Shows the status" }