System Hardening

Introduction

System Hardening goes beyond basic security practices. It involves aggressively locking down the operating system to minimize its attack surface. This is often required for servers processing financial data (PCI-DSS compliance) or healthcare records (HIPAA).

1. Principle of Least Privilege

Never run web servers (like Nginx, Node.js, or Tomcat) as the root user. If an attacker exploits a vulnerability in your Node.js application, they will gain whatever privileges the Node process has. If it runs as root, the attacker owns the entire server.

Always create a dedicated, unprivileged user for your applications:

sudo adduser --system --no-create-home myappuser

2. Disable Unused Services and Ports

Every open port is a potential entry point for an attacker. Use ss -tulnp to see exactly which services are listening on which ports. If you are not using a service, stop and disable it.

# Stop the service immediately
sudo systemctl stop apache2

# Prevent it from starting when the server reboots
sudo systemctl disable apache2

3. Secure Shared Memory

Shared memory can be used in an attack to execute arbitrary code. You should mount /run/shm as read-only or restrict execution. Add this line to your /etc/fstab file:

tmpfs   /run/shm    tmpfs   defaults,noexec,nosuid  0 0

4. Install Fail2Ban

Fail2Ban is an intrusion prevention software framework that protects computer servers from brute-force attacks. It monitors log files (like /var/log/auth.log) and dynamically updates firewall rules to ban IP addresses that show malicious signs, such as too many password failures.

sudo apt install fail2ban
sudo systemctl enable fail2ban

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