Linux Server Hardening Best Practices

Server hardening is the process of securing a server by reducing its attack surface and minimizing potential vulnerabilities. This guide covers essential practices for hardening Linux servers.

Initial Setup

1. Keep System Updated

• Regularly update packages: `apt update && apt upgrade`
• Enable automatic security updates
• Monitor security advisories for your distribution

2. Remove Unnecessary Software

• Uninstall unused packages and services
• Disable unnecessary system services
• Remove default user accounts if not needed

User Management

3. Secure User Accounts

• Use strong passwords or SSH keys
• Disable root login via SSH
• Implement password policies
• Use sudo instead of direct root access
• Regularly audit user accounts

4. SSH Security

• Change default SSH port (optional but recommended)
• Disable password authentication, use keys only
• Implement fail2ban to prevent brute force attacks
• Use strong encryption algorithms
• Limit SSH access to specific IPs if possible

Network Security

5. Firewall Configuration

• Use UFW or firewalld to manage firewall rules
• Only open necessary ports
• Block all incoming traffic by default
• Allow only specific services

6. Network Services

• Disable unused network services
• Use secure protocols (HTTPS, SSH)
• Implement rate limiting
• Monitor network connections

System Hardening

7. File System Security

• Set proper file permissions (chmod, chown)
• Use filesystem encryption for sensitive data
• Implement disk quotas
• Regular filesystem integrity checks

8. Kernel Parameters

• Configure sysctl for security
• Disable IP forwarding if not needed
• Enable SYN flood protection
• Configure connection tracking

Monitoring and Logging

9. System Logging

• Configure centralized logging
• Monitor system logs regularly
• Set up log rotation
• Implement log analysis tools

10. Intrusion Detection

• Install and configure AIDE or Tripwire
• Set up file integrity monitoring
• Implement intrusion detection systems (IDS)
• Regular security audits

Additional Security Measures

• Enable SELinux or AppArmor
• Use encrypted backups
• Implement two-factor authentication
• Regular security patches
• Network segmentation
• Regular security audits and penetration testing