Could somebody give some simple steps with configuration example how to setup simple firewall on Ubuntu (using console only)? Only ssh, http and https access should be allowed.
Use this script.
Just decide if you want to allow incoming ICMP (ping) or not.
# Clear any existing firewall stuff before we start iptables --flush iptables -t nat --flush iptables -t mangle --flush # As the default policies, drop all incoming traffic but allow all # outgoing traffic. This will allow us to make outgoing connections # from any port, but will only allow incoming connections on the ports # specified below. iptables --policy INPUT DROP iptables --policy OUTPUT ACCEPT # Allow all incoming traffic if it is coming from the local loopback device iptables -A INPUT -i lo -j ACCEPT # Accept all incoming traffic associated with an established # connection, or a "related" connection iptables -A INPUT -i eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT # Allow incoming connections # SSH iptables -A INPUT -p tcp -i eth0 --dport 22 -m state --state NEW -j ACCEPT # HTTP iptables -A INPUT -p tcp -i eth0 --dport 80 -m state --state NEW -j ACCEPT # HTTPS iptables -A INPUT -p tcp -i eth0 --dport 443 -m state --state NEW -j ACCEPT # Allow icmp input so that people can ping us iptables -A INPUT -p icmp -j ACCEPT # Reject all other incoming packets iptables -A INPUT -j REJECT
As noted in comments to another answer, you don't want to lose your connection before you allow the ssh port. From the man page:
When running ufw enable or starting ufw via its initscript, ufw will flush its chains. This is required so ufw can maintain a consistent state, but it may drop existing connections (eg ssh). ufw does support adding rules before enabling the firewall, so administrators can do:
ufw allow proto tcp from any to any port 22
before running ’ufw enable’. The rules will still be flushed, but the ssh port will be open after enabling the firewall. Please note that once ufw is ’enabled’, ufw will not flush the chains when adding or removing rules (but will when modifying a rule or changing the default policy)."
So here is an approach that uses a script to set it. You will get logged out when you run this script, but having run it you can then log in again over ssh.
Put the following in a script and call it start-firewall.sh
#!/bin/sh ufw allow ssh ufw enable ufw default deny ufw allow http ufw allow https
And then make it executable and run it by doing
$ chmod + x start-firewall.sh $ sudo ./start-firewall.sh
To learn more, read the man page.
If you familiarize yourself with scripting
iptables, you will have full control over all firewall capabilities. It's nowhere near as friendly as Firestarter, but it can be done at the console with
vi editors. Check out this tutorial geared towards Ubuntu.
Quicktables helped me to learn iptables rules. Just run the script and it will generate an iptables script for you... then you can open it and view the associated commands generated by the questions it asked of you. It's a great learning resource.
Unfortunately, it is no longer maintained.
To create setup rules you like you would need to edit the file /etc/default/firehol and change START_FIREHOL=YES
And you would want to make your /etc/firehol/firehol.conf look like this.
version 5 interface any IfAll client any AnyClient accept server "ssh http https" accept # Accept everything from trusted networks server anystateless AllInside accept src "10.3.27.0/24"
One of the great things about firehol is the 'try' command. You can adjust your configuration file and do a 'firehol try', if you where connected via ssh, and something about what you changed killed your network access then firehol will revert the changes. To have the changes actually go into effect, you must say commit.
I would prefer Shorewall. It is easy to setup but flexible at the same time.
Maybe you should take a look at http://iptables-tutorial.frozentux.net/iptables-tutorial.html. Also you can find more information on lartc.org