Enterprise Linux Server Hardening (CIS Benchmarks)
In the world of enterprise IT, a default Linux installation is never secure enough for production. To protect critical infrastructure from modern cyber threats, organizations rely on the CIS (Center for Internet Security) Benchmarks. Here are the core foundational steps to harden your Linux servers based on these industry standards.
1. Secure SSH Access
SSH is the most common entry point for attackers. Hardening the SSH daemon (sshd_config) is your absolute first priority:
- Disable Root Login: Set
PermitRootLogin no. Admins should log in as a standard user and elevate privileges usingsudo. - Disable Password Authentication: Set
PasswordAuthentication noand strictly enforce SSH Key-based authentication (like Ed25519 keys). - Change Default Port: Moving away from Port 22 reduces automated brute-force bot attacks.
2. Network Configuration & Firewalls
Never expose a server to the internet without a strict firewall policy. Use UFW or firewalld to implement a "Default Deny" policy.
sudo ufw default deny incoming
sudo ufw default allow outgoing
sudo ufw allow 2222/tcp
sudo ufw enableAdditionally, disable unused network protocols like IPv6 (if not in use) and ensure IP forwarding is disabled unless the server acts as a dedicated router.
3. Disable Unused Filesystems and Services
Every running service is a potential vulnerability. Reduce your attack surface by disabling legacy filesystems (like cramfs, freevxfs) and stopping services you don't need. You can use systemctl disable to ensure they don't start on boot.
4. Implement Audit Logging (auditd)
You cannot secure what you cannot monitor. The auditd service tracks system events, file access, and user commands. Configure audit rules to log events such as changes to /etc/passwd, failed login attempts, and modifications to network configurations.
Summary
Server hardening is not a one-time setup; it is a continuous process of auditing, patching, and monitoring. By adhering to CIS Benchmarks, you establish a zero-trust foundation that drastically mitigates the risk of infrastructure compromise.