Linux Hardening Guide
1. Keep the System Updated
Regularly update the operating system and installed packages using package managers like:
Debian/Ubuntu: sudo apt update && sudo apt upgrade
RHEL/CentOS: sudo yum update
Arch Linux: sudo pacman -Syu
Enable automatic updates when possible.
2. Minimize Installed Packages
Remove unnecessary packages and services to reduce vulnerabilities.
Use apt purge, yum remove, or pacman -Rns to uninstall unused software.
3. User and Access Control
Disable root login and use sudo for administrative tasks.
Set strong passwords and enforce password policies.
Use the principle of least privilege (POLP) for user accounts.
4. Secure SSH
Change the default SSH port (e.g., from 22 to another port in /etc/ssh/sshd_config).
Disable root login via SSH (PermitRootLogin no).
Enable key-based authentication and disable password authentication (PasswordAuthentication no).
Use firewall rules to restrict SSH access (e.g., using iptables or ufw).
5. Configure a Firewall
Use iptables, firewalld, or ufw to manage firewall rules.
Allow only necessary inbound and outbound traffic.
Example: sudo ufw allow 22/tcp (if using SSH on port 22).
6. Implement Security Modules
Enable SELinux (on RHEL-based systems) or AppArmor (on Debian-based systems) for mandatory access control.
Example:
Check SELinux status: sestatus
Enable AppArmor: sudo systemctl enable apparmor
7. Monitor and Log Activities
Enable and configure system logging using rsyslog or journalctl.
Use tools like auditd for detailed auditing.
Regularly review logs in /var/log/ for suspicious activity.
8. Use Intrusion Detection and Prevention Systems
Install and configure tools like:
Fail2Ban to block brute-force attacks.
AIDE (Advanced Intrusion Detection Environment) for file integrity monitoring.
9. Encrypt Data and Communications
Use LUKS for disk encryption.
Ensure sensitive communications use TLS/SSL (e.g., HTTPS, OpenVPN).
Secure sensitive files with GPG encryption.
10. Backup and Disaster Recovery
Regularly back up important files and system configurations.
Use tools like rsync, tar, or Timeshift for backups.
Store backups securely and test recovery procedures periodically.
Conclusion
Following these hardening steps will significantly improve the security of a Linux system. Security is an ongoing process, so regular monitoring and updates are essential to maintaining a secure environment.