15.3 Ubuntu Services and iptables Rules

By default, a newly installed Ubuntu system does not have any iptables rules defined to restrict access to ports. To view the current iptables settings, the following command may be executed in a terminal window:

# iptables -L

Chain INPUT (policy ACCEPT)

target prot opt source destination

 

Chain FORWARD (policy ACCEPT)

target prot opt source destination

 

Chain OUTPUT (policy ACCEPT)

target prot opt source destination

As illustrated in the above output, no rules are currently defined. Whilst this may appear to be an unsafe configuration it is important to keep in mind that a newly installed Ubuntu system also has few services running by default, making the ports essentially useless to a potential attacker. It is not possible, for example, to remotely log into a newly installed Ubuntu system or access a web server for the simple reason...