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- Blocking portscan
- # Attempt to block portscans
- # Anyone who tried to portscan us is locked out for an entire day.
- iptables -A INPUT -m recent --name portscan --rcheck --seconds 86400 -j DROP
- iptables -A FORWARD -m recent --name portscan --rcheck --seconds 86400 -j DROP
- # Once the day has passed, remove them from the portscan list
- iptables -A INPUT -m recent --name portscan --remove
- iptables -A FORWARD -m recent --name portscan --remove
- # These rules add scanners to the portscan list, and log the attempt.
- iptables -A INPUT -p tcp -m tcp --dport 139 -m recent --name portscan --set -j LOG --log-prefix "Portscan:"
- iptables -A INPUT -p tcp -m tcp --dport 139 -m recent --name portscan --set -j DROP
- iptables -A FORWARD -p tcp -m tcp --dport 139 -m recent --name portscan --set -j LOG --log-prefix "Portscan:"
- iptables -A FORWARD -p tcp -m tcp --dport 139 -m recent --name portscan --set -j DROP
- Spoofed/Invalid packets
- # Reject spoofed packets
- # These adresses are mostly used for LAN's, so if these would come to a WAN-only server, drop them.
- iptables -A INPUT -s 10.0.0.0/8 -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 127.0.0.0/8 -j DROP
- #Multicast-adresses.
- iptables -A INPUT -s 224.0.0.0/4 -j DROP
- iptables -A INPUT -d 224.0.0.0/4 -j DROP
- iptables -A INPUT -s 240.0.0.0/5 -j DROP
- iptables -A INPUT -d 240.0.0.0/5 -j DROP
- iptables -A INPUT -s 0.0.0.0/8 -j DROP
- iptables -A INPUT -d 0.0.0.0/8 -j DROP
- iptables -A INPUT -d 239.255.255.0/24 -j DROP
- iptables -A INPUT -d 255.255.255.255 -j DROP
- # Drop all invalid packets
- iptables -A INPUT -m state --state INVALID -j DROP
- iptables -A FORWARD -m state --state INVALID -j DROP
- iptables -A OUTPUT -m state --state INVALID -j DROP
- Block Smurf attacks
- # Stop smurf attacks
- iptables -A INPUT -p icmp -m icmp --icmp-type address-mask-request -j DROP
- iptables -A INPUT -p icmp -m icmp --icmp-type timestamp-request -j DROP
- iptables -A INPUT -p icmp -m icmp -j DROP
- # Drop excessive RST packets to avoid smurf attacks
- iptables -A INPUT -p tcp -m tcp --tcp-flags RST RST -m limit --limit 2/second --limit-burst 2 -j ACCEPT
- Block ICMP (aka ping)
- # Don't allow pings through
- iptables -A INPUT -p icmp -m icmp --icmp-type 8 -j DROP
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