How to secure a server

To enjoy maximum freedom of configuration, the best solution is to host your own server. Another good alternative is to use Dedicated Root Servers, which can be rented by many hosts and grant access to the root account. The basic administrative steps such as installation, structuring, and maintenance of the server remain within the tenant’s sphere of responsibility, as would be the case with a self-hosted variant. This type of server package usually only takes care of the initial installation of the operating system, if needed.

Regardless of the chosen hosting solution, you should be careful and responsible when designing and using the root account. In particular, the issue of security plays an important role here: On the one hand, a faulty procedure in the root area is particularly difficult, on the other hand, a concrete basis for a stable, high-performance and secure server can be created if the procedure is correct. For example, in order to secure a dedicated server and protect it against external access, a mandatory password change is just one of the many necessary measures to increase server security.

Even before you start with the actual precautions and configure your server safely, you can influence the future security potential of your web project. Regardless of whether you choose a Windows or a Linux system, the following principle applies to the installation: A server should only contain the software it needs to perform its tasks. The reason for this is that any installed application is a potential security risk and can have a negative impact on performance. To offer attackers as little as possible, you should only install or activate the necessary system components, and only access verified third-party software.

After the installation, you should first set a root password (Linux systems). As standard, there is no value defined and the administrator account is also blocked until you make a corresponding entry. After installation, the operating system usually automatically prompts you to create a user account, including a password, which is the root access point. If you rented a server from a provider and received an existing root log-in, you must change the password. To do this, you must log into your server via SSH (from a Linux system) or PuTTY (from a Windows system) and enter the following command in the proper terminal for a root log-in to change the password:

You can then specify your password, which then requires verification. Be sure to choose the longest possible password, not just letters but also special characters and numbers. In addition, it is recommended to use a password manager to save the password, so that you can access it at any time. Then, try to connect to the new root log-in. If it’s done correctly, you can disconnect the SSH connection made at the beginning.

To secure your server, it is also recommended to disable the direct SSH log-in for the root account. If not, an attacker who possesses the password could use the remote account to remotely access the server, and block the SSH direct log-in for the root account. Before you can perform this action, you must have at least one additional user account that can be connected to the server, in addition to the root user, and which is not completely excluded from the system. If you have not made a corresponding user profile, use the following command to create it:

With this, you can create the user account user1, which is also added to the users group (-g). As well as that, the home directory /home/user1 is assigned to this user profile (-d). The command specifies the bash shell as the default shell (-s /bin/bash). Finally, define a secure password for this new log-in account:

Now, test whether the login works with the created user account and only proceed with the actual project (locking yourself out of the root account) if you are successful.  For this, you need the SSH configuration sshd_config, which you can open with your preferred editor. Look for the ‘PermitRootLogin yes’ entry and replace it with ‘PermitRootLogin no’. After restarting the SSH service via command line:

You can also use the AllowGroups line in the configuration file to determine which users are allowed to connect to the server via SSH. To do this, simply create a group (addgroup) and add the desired users (adduser). Then add the selected group name to the sshd_config (e. g. AllowGroups ssh_user).

However, in the event of SSH access to your server, you should keep an eye on all remote activities. This allows you to determine if you have secured the SSH service on your server properly. Additionally, monitoring these activities means that you are warned at an early stage by a good monitoring of the established connections in case of unauthorized access and can take appropriate countermeasures. A simple shell script is sufficient for this, which automatically sends a notification email to your address on every successful remote login on your server.

A corresponding script (here: /opt/shell-login.sh), which you can easily create yourself, must contain the following code for this purpose:

Then add the following line to the /etc/profile profile file:

This entry can ensure that the script is executed and, in the event of a successful log-in, it sends a notification mail to the desired address. The prerequisite is that the script is assigned the right 755, which can be done with the following command:

In general, there is no software that is completely free of the vulnerabilities mentioned in the previous section. However, cybercriminals would first have to discover the exploitable mis-programming before they can take up the attack. As a rule, known vulnerabilities are quickly closed again by published updates. If you keep on top of updates to the operating system and the installed programs, and update as soon as possible, you are ensuring the best possible protection for your server. Nearly all server systems also allow you to download and install important security updates automatically in the background.

For example, if you want to secure a Windows server that receives automatic updates, you can set specific instructions for the update process in the Windows Update area. In this way, you can configure when and how regularly to check for updates, whether you want updates to be installed, and when the system should reboot. There are specific scripts such as apt-listchanges or apticron for Linux systems, which inform you daily about new available software packages and allow you to download them. Other scripts, such as unattended upgrades, will then download the automatic installation.

Hackers, who want to access your server or the applications running on them, have different options to do this. One of the simplest and most frequently used types of attack is the so-called brute-force method. The attacker tries to access passwords using a tool that attempts to log in one at a time. However, the more care you put into assigning your password, the less likely this method will be to succeed. Do keep in mind that, particularly if you are offering a service with a registration option, you must assume that not every user will be as conscientious and cautious as needed. There is of course, no need for complex, expensive software to protect against such attacks. Since every log-in attempt is registered, answered, and recorded in log files, simple analysis tools can help.
Fail2ban (Linux-/POSIX-Systems) or RdpGuard (Windows) check the relevant log files, detect unusual behavior, and block the IP address of suspicious users.

With the recommended configuration suggestions, server security significantly increases. The various settings for the login process and the restriction of the root account give your server a very high security standard, in conjunction with continuous updates, monitoring tools, and mandatory security software. However, even the best configuration and dedicated care cannot provide one hundred percent protection for the server. Program errors, hardware failures, or personal negligence can lead to data being lost in the worst case. A further supporting pillar of your security system should be the appropriate backup strategy that allows you to restore the appropriate files in such a case.

There is no lack of powerful tools that can support you not only when creating, but also when importing a backup copy. A free application which should be mentioned here is the synchronization program rsync, which takes its name from the same protocol and is available in various forms for almost all common platforms (macOS, Windows, Linux). This tool keeps a copy of your server data up-to-date by noting all changes to the original in real time. As well as a general backup of the server, the program also automatically protects the database.