While we continue to see the WannaCry and other malware around, I thought I would secure my own network. Since I allow visitors onto their networks, I figured I would configure all new DHCP’d hosts to access the Internet only via HTTP and HTTPs and not allow them to use any DNS servers other than OpenDNS. Here’s how to do it:
The first thing I did was create an access restriction. I did this just to see what chain would be created and I would put subsequent rules into that chain.
The previous screenshot created this chain:
Chain rdev07 (1 references)
target prot opt source destination
DROP all -- 192.168.0.15 anywhere
With this chain, I can add additional rules. The first thing I want to do is allow only DNS access to OpenDNS servers and none other. For this, I would run the following commands:
iptables -A rdev07 -4 -p tcp -s 192.168.0.0/24 -d 208.67.222.222/32 --dport 53 -j ACCEPT
iptables -A rdev07 -4 -p udp -s 192.168.0.0/24 -d 208.67.222.222/32 --dport 53 -j ACCEPT
iptables -A rdev07 -4 -p tcp -s 192.168.0.0/24 -d 208.67.220.220/32 --dport 53 -j ACCEPT
iptables -A rdev07 -4 -p udp -s 192.168.0.0/24 -d 208.67.220.220/32 --dport 53 -j ACCEPT
iptables -A rdev07 -4 -p tcp -s 192.168.0.0/24 -d 0.0.0.0/0/0 --dport 53 -j REJECT
iptables -A rdev07 -4 -p udp -s 192.168.0.0/24 -d 0.0.0.0/0/0 --dport 53 -j REJECT
These rules basically allow DNS queries from my network to the 2 OpenDNS servers. The last 2 rules mean that no other DNS servers outside of those 2 servers can be queried. The reason I do this is because there is some malware out there that will change the DNS servers to query on Windows, effectively overriding the DHCP setting. An alternative to this would be to configure Tomato to intercept DNS requests, but I would rather do it this way.
I added the following rules because I had noticed for some reason that some connections coming back from OpenDNS were dropped. I think they’re optional, but I put them in.
iptables -A rdev07 -4 -p tcp -s 208.67.222.222/32 -d 192.168.0.0/24 --sport 53 -j ACCEPT
iptables -A rdev07 -4 -p udp -s 208.67.222.222/32 -d 192.168.0.0/24 --sport 53 -j ACCEPT
iptables -A rdev07 -4 -p tcp -s 208.67.222.222/32 -d 192.168.0.0/24 --sport 53 -j ACCEPT
iptables -A rdev07 -4 -p udp -s 208.67.222.222/32 -d 192.168.0.0/24 --sport 53 -j ACCEPT
Next, I go to create my whitelist – this would be my iPhone, iPad, android, etc – any hosts that I trust. I’m going to allow these host to go out to any host with TCP and UDP.
iptables -A rdev07 -4 -p tcp -s 192.168.0.3/32 -d 0.0.0.0/0 -j ACCEPT
iptables -A rdev07 -4 -p tcp -s 192.168.0.11/32 -d 0.0.0.0/0 -j ACCEPT
iptables -A rdev07 -4 -p tcp -s 192.168.0.31/32 -d 0.0.0.0/0 -j ACCEPT
iptables -A rdev07 -4 -p udp -s 192.168.0.3/32 -d 0.0.0.0/0 -j ACCEPT
iptables -A rdev07 -4 -p udp -s 192.168.0.11/32 -d 0.0.0.0/0 -j ACCEPT
iptables -A rdev07 -4 -p udp -s 192.168.0.31/32 -d 0.0.0.0/0 -j ACCEPT
I know that they can still get viruses. I hope they don’t. They can only use OpenDNS for DNS services, but they can access basically anything outside on any port.
Lastly, I configure the rules to allow only HTTP and HTTPs out.
iptables -A rdev07 -4 -p tcp -s 192.168.0.0/24 -d 0.0.0.0/0 --dport 80 -j ACCEPT
iptables -A rdev07 -4 -p tcp -s 192.168.0.0/24 -d 0.0.0.0/0 --dport 443 -j ACCEPT
iptables -A rdev07 -4 -p all -s 192.168.0.0/24 -d 0.0.0.0/0 -j DROP
With this, anyone else on the network can connect to port 80 and 443 of any host on the Internet. Then, any traffic going out to any other port is dropped.
After testing all commands and seeing that they worked for me, I put them all into Administration/Scripts/Firewall.
Have fun and be safe! Please post any comments below.
