Linux server hardening consists of best measures and practices to reduce vulnerabilities and improve server security. Linux security and server hardening core principles include the least privilege, segmentation, and reduction. The principle of least privileges implies that users and processes get the bare minimum of permission to conduct the tasks. The following principle of segmentation involves splitting more extensive areas into smaller ones. It generally applies to memory usage, and each process can access its memory segments. The reduction principle seeks to remove something that the system does not strictly need to work.
Hardening is done on different levels. It ranges from the physical level, by restricting access to unauthorized accounts, to the application level, by removing unwanted or unsolicited attempts. Some of the best practices for Linux security and server hardening include:
Use Strong and Unique Passwords
For any secure server, setting strong passwords is crucial. It is recommended to set a password of at least ten characters and use special characters, upper and lowercase letters. It would be best not to use the same password for multiple users or software systems. Also, remember to configure expiration for your password to remind you to change passwords at regular intervals. For Linux platforms, various excellent password managers are available, offering multiple features such as multi-factor authentication, password generators, and Cloud password storage. Strong passwords render it difficult for automated tools to guess the password and trigger malicious attempts.
Install security updates and patches
Implementing regular software patches for your Linux server enables it to address emerging vulnerabilities proactively. Most of the system weaknesses are triggered by flaws in software. Software patch management helps to reduce these risks. Most Linux users neglect the crucial task of putting the patches into action. If they do not facilitate prompt updates, the bad actors can hack the system. Most Linux distributions provide the option to limit the packages you want to upgrade.
Use Secure Shell (SSH)
Strong passwords are the cornerstone for securing your Linux server. However, other more robust methods are available that will allow you to log into the private servers securely. Secure shell (SSH) is a secure protocol that uses encryption technology to facilitate communication with the server. SSH key pairs make it difficult for cybercriminals to hack systems by brute force. SSH enables a user to run shell commands to a server remotely. It is a step up from Telnet, which performs the same action but does not use an encrypted connection, leading to security breaches. SSH key pair is equivalent to a 12-character password. Configure each server to use SSH for logging in remotely, and also ensure that you are configuring IPTables to restrict SSH access from recognized IPs only.
Implementing a firewall enables you to allow only selected traffic to enter the system. Enabling firewall solutions such as iptables or the newer nftables will help you. The use of Linux iptables will enable you to keep a tab on incoming, outgoing, and forwarded practices to facilitate server security. Configuring “allow” and “deny” rules for accepting or sending traffic from specific IP addresses will help you make your server more secure. Firewall implementation enables you to restrict unchecked traffic movement. The “deny all, allow some” policy is useful for incoming traffic, to share only the required services.
Purge Unnecessary Packages
It is essential to keep the system clean. Overcrowding your system also increases the backup and restore times and may make it vulnerable to various threats. Purging the Linux system of unnecessary packages enables you to leverage a healthy and secure method. OS generally comes with preloaded software and services that constantly run in the background. List down the packages and software installed on your servers using the package managers, delete unnecessary and unused packages, and clean up old home directories.
Close Hidden Open Ports
Using the ‘netstat’ networking command, you can view all open ports and other associated programs. Open ports tend to reveal network architecture data and extend attack surfaces. The netstat command helps determine which ports are listening and shows the currently available connection details.
These tips and tricks will enable you to maximize your server security. Taking additional efforts to secure your Linux server will keep your Linux server secure against the ever-evolving cyber threat attempts. Linux hardening and server security is an ongoing journey that allows you to improve system security levels and maximize server usability and performance.