I am running Ubuntu 10.04.
Here are the IPv4 firewall rules that I've been using now for a few months:
*filter #Allow all loopback (lo0) traffic and drop all traffic to 127/8 #that doesn't use lo0 -A INPUT -i lo -j ACCEPT -A INPUT -d 127.0.0.0/8 -j REJECT #Accept all established inbound connections -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT #Allow all outbound traffic - you can modify this to only allow certain traffic -A OUTPUT -j ACCEPT #Allow HTTP and HTTPS connections from anywhere (the normal ports #for websites and SSL) -A INPUT -p tcp --dport 80 -j ACCEPT -A INPUT -p tcp --dport 443 -j ACCEPT #Allow SSH connections #The -dport number should be the same port number you set in sshd_config -A INPUT -p tcp -m state --state NEW --dport 22 -j ACCEPT #Allow ping -A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT #Log iptables denied calls -A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7 #Reject all other inbound - default deny unless explicitly allowed policy -A INPUT -j REJECT -A FORWARD -j REJECT COMMIT
These rules seem to have served me well. I'm only running an Apache web server, and only allow HTTP and HTTPS connections. I also allow my server to be pinged.
First question: Do you think these IPv4 are secure enough? Is there any further room for hardening?
Recently, I activated IPv6 on my server. Correspondingly, I created firewall rules for IPv6 that are exactly the same as the above, except that I changed
-A INPUT -d 127.0.0.0/8 -j REJECT
-A INPUT -d ::1 -j REJECT
-A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT
-A INPUT -p icmpv6 -j ACCEPT
These new IPv6 rules seem to be working fine. But I'm not sure. IPv6 is a lot more complex, so I may well be overlooking something.
Question 2: Can these IPv6 rules be hardened further?
In case you're wondering, I have the above IPv4 and IPv6 rules in their two separate
/etc/ip6tables.firewall.rules files, and activate them at boot by using
iptables-restore < /etc/iptables.firewall.rules
ip6tables-restore < /etc/ip6tables.firewall.rules