Linux servers are renowned for their stability, cost-effectiveness, and open-source nature. However, ensuring security is of utmost importance due to ever-evolving cyber threats and attacks. This guide presents an ultimate Linux server security checklist that covers essential steps to harden and secure a Linux server, providing explanations on the importance of each step and how it helps maintain system integrity and safeguard valuable data. We encourage you to use this checklist as a reference for achieving ultimate security on their Linux servers. The steps are sorted from most important to least important.
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Harden SSH: Securing your SSH connection is crucial for remote server access and management. Proper SSH configuration prevents unauthorized access. Recommendations include disabling root login, employing key-based authentication, and changing the default SSH port.
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Set Up a Basic Firewall: A firewall is essential for controlling incoming and outgoing network traffic. Configuring a basic firewall using tools such as UFW (Uncomplicated Firewall) or firewalld helps defend your server against unauthorized access and malicious attacks.
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Create a Limited Privilege Administrative User: Establishing a user with sudo permissions is vital for Linux server hardening. A sudo user has administrative access but operates with standard user permissions by default. Limiting privileges minimizes potential damage from accidental or malicious actions, as elevated permissions are granted only when necessary.
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Keep Kernel and Packages Up-to-Date: Regularly updating your kernel and installed packages ensures protection against known vulnerabilities. Use package management tools like 'yum' or 'apt' to check for and apply updates.
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Enable Security-Enhanced Linux (SELinux): Activating SELinux provides an additional security layer by enforcing mandatory access controls. Enabling SELinux helps prevent unauthorized users or applications from performing actions that could compromise the server.
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Configure fail2ban: Fail2ban is a log-parsing application that automatically updates firewall rules to block IP addresses exhibiting suspicious behavior, such as multiple failed login attempts. Installing and customizing fail2ban protects your server from brute-force attacks.
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Disable Unneeded Services: Minimizing the attack surface of your server involves disabling services that are not required for its function. Utilize tools like 'systemctl' to list and manage services, and deactivate those that are unneeded.
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Remove Unused Packages: Eliminating unused packages reduces your server's attack surface. Regularly review installed packages and remove those that are no longer necessary.
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Enforce Strong Password Policies: Requiring strong passwords with minimum length and complexity standards reduces the risk of unauthorized access through password guessing or brute-force attacks.
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Implement Password Expiration: Password aging policies that require users to change their passwords periodically help maintain password security. Configure the 'chage' command to enforce password expiration and warning periods.
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Prevent Old Password Reuse: Restricting the reuse of previous passwords helps maintain password security over time. Configure the 'PAM' module to enforce password history limitations.
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Restrict USB and Thunderbolt Device Access: Preventing access to USB and Thunderbolt devices stops unauthorized users from connecting external devices to your server, reducing the risk of data theft or malware introduction.
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Limit Privilege Escalation Binaries: Set User ID (SUID) and Set Group ID (SGID) binaries pose security risks, as they allow users to execute commands with elevated privileges. Identify and restrict unnecessary SUID and SGID binaries to minimize potential vulnerabilities.
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Disable ICMP: Turning off Internet Control Message Protocol (ICMP) can protect your server from denial-of-service (DoS) attacks that exploit ICMP to flood the server with traffic. Modify the firewall settings to disable ICMP.
Achieving ultimate security on your Linux server involves a combination of hardening measures, best practices, and consistent maintenance. By following this checklist, you take a proactive approach to securing your server against various cyber threats. Remember that security is an ongoing process, and it's crucial to stay informed about new vulnerabilities and emerging security trends. Regularly review and update your security measures to ensure your Linux server remains protected and performs optimally.