How to make your instance more secure?
This post is obviously not complete security guide and it’s not meant to be. However I want to talk about some basics which I think are minimum in subject of securing our Linux. I must emphasize that you have complete control of your instance and it’s your responsibility to take care about security of your data and your site users. I definitely encourage to constantly learn about server administration.
One of the most important things are regular updates of the system and other installed software. Unfortunately vulnerabilities happened everywhere (famous example of vulnerability in OpenSSL library from 2014) so we should install every security updates as fast as possible. Before we continue let’s update our system.
The first step will be following command:
sudo apt-get update
In this way we ensure that our system “knows” about all the updates available but nothing will be installed yet.
Next we can do this:
sudo apt-get upgrade
sudo apt-get dist-upgrade
There is significant difference between those two. In first case only packages that were already installed will be updated. However common practice is that one package depends on others. If new version of installed software depends on package which was not required previously and this package is not available in system, update will fail. All information about the problems will be printed to the console.
In second case dependencies are resolved automatically and some packages can be deleted or new packages can be installed. Now it really doesn’t matter because we just launch our instance and we don’t using it for any purpose yet. However when we start web server, database and our site will be made public, we won’t want something stop working because of update. It doesn’t mean of course that we shouldn’t update our system. It only means that we always need to know what we are doing and why. We probably should consider launching stage environment and check any modifications there first. In AWS ecosystem it’s really easy to duplicate EC2 instance.
Some of you probably notice that though installation of all updates, OpenSSL library which I mention remains in version 1.0.1f, which is theoretically vulnerable to HeartBleed attack. In fact it’s not true. This version was patched by Ubuntu maintainers the same day which vulnerability was disclosed. More information here.
Now we should reboot our instance.
When you run this command your connection will be interrupted. Wait minute or two and try to connect again.
Change the default SSH port
It’s worth to consider change the default SSH port from 22 to some other number grater than 1023. Many bots which are used to automatic attacks search for open SSH port, but they limit themselves to default port. It of course won’t stop all intrusion attempts but can help reduce the number of them. We can change port in SSH configuration file. We must edit it as root so we run command:
sudo nano /etc/ssh/sshd_config
Of course you can use your favorite text editor instead of nano. 🙂
Lets find following line in file
and change the value to something else, for example:
Now save changes (in nano ctrl+O and confirm hitting enter) and exit editor (in nano ctrl+X). We should restart SSH service to reload configuration:
sudo service ssh restart
Our current connection should not be interrupted but from now on every new connection to our instance must be on port which we put to config file. As you remember we define some security rules in our EC2 dashboard so we need to go back there and open up this port.
In group “Network & Security” we need to find tab called “Security Groups” and then right click group which our instance belongs to. From menu choose “Edit inbound rules”. Now in place of SSH we select “Custom TCP Rule” and enter the new port number. Remember to save the changes.
Powinno być już możliwe nawiązanie nowego połączenia. Jeśli łączymy się z konsoli musimy dodać parametr “-p” i dopisać po nim numer portu, a więc w moim przypadku będzie to:
Now we should be able to start new connection. If you’re using console you should add “-p” followed by port number. In my case it will be:
ssh -i ~/.ssh/test1-keys.pem firstname.lastname@example.org -p 56321
If you’re connecting by putty, find on list of saved sessions your instance and load settings. Now you should change port number and save your session again.
After this part our system is up to date and SSH works on different than default port number. As I mention it’s not guarantee that you are 100% secure. I recommend that you read about some tools which can help you in process of hardening your system. In next part we’ll install software which is essential to run our virtual machine as web server.