Implement Server Hardening with CIS Benchmarks

The Center for Internet Security (CIS) Benchmarks are industry-standard best practices for securing operating systems, applications, and cloud environments. Implementing CIS benchmarks ensures:

✅ Hardened server configurations against cyber threats.
✅ Compliance with security frameworks like NIST, ISO 27001, and PCI-DSS.
✅ Reduced attack surface by eliminating misconfigurations and vulnerabilities.
✅ Automated security auditing to enforce best practices.

By applying CIS benchmarks, you enhance security, maintain compliance, and proactively defend against threats.

How to Implement CIS Benchmarks for Linux Servers

1. Download the CIS Benchmark for Your OS

1. Visit the CIS Website:

   • CIS Benchmarks

2. Download the benchmark for your Linux distribution (Ubuntu, Debian, CentOS, RHEL).

3. Review the recommendations and implement the security settings manually or with automation tools.

2. Automate Benchmarking with CIS-CAT Pro or Lynis

To scan for security misconfigurations, use CIS-CAT Lite (free) or Lynis.

Option 1: Install and Run CIS-CAT Lite

1. Download CIS-CAT Lite from CIS Workbench.

2. Extract and run the tool:

   tar -xvf CIS-CAT-Lite.tar.gz
   cd CIS-CAT-Lite
   ./cis-cat.sh -a
   

3. Review the security audit report and apply recommendations.

Option 2: Use Lynis for Automated Auditing

Lynis is a lightweight and open-source security auditing tool.

1. Install Lynis:

   sudo apt install lynis -y   # Debian/Ubuntu
   sudo yum install lynis -y   # CentOS/RHEL

2. Run a full system security audit:

   sudo lynis audit system
   

3. Review the security report:

   cat /var/log/lynis-report.dat
   

4. Apply CIS security recommendations based on the audit findings.

3. Implement Key CIS Security Hardening Recommendations

A. Restrict Root Access and Enforce Least Privilege

• Disable root login via SSH:

  sudo nano /etc/ssh/sshd_config
  

  Change:

  PermitRootLogin no
  

  Restart SSH:

  sudo systemctl restart sshd
  

• Enforce sudo authentication:

  sudo visudo
  

  Ensure:

  Defaults timestamp_timeout=5
  

B. Enable Strong Authentication Policies

• Enforce password complexity:

  sudo nano /etc/security/pwquality.conf
  

  Set:

  minlen = 12
  minclass = 3
  

• Enable automatic account lockout after failed logins:

  sudo nano /etc/pam.d/common-auth
  

  Add:

  auth required pam_tally2.so onerr=fail deny=5 unlock_time=900
  

C. Harden Network Security

• Disable unused network services:

  sudo systemctl disable avahi-daemon
  sudo systemctl disable cups
  

• Enforce firewall rules:

  sudo ufw allow 22
  sudo ufw allow 80
  sudo ufw allow 443
  sudo ufw enable
  

• Restrict incoming connections with iptables:

  sudo iptables -A INPUT -p tcp --dport 22 -s 192.168.1.0/24 -j ACCEPT
  sudo iptables -A INPUT -p tcp --dport 22 -j DROP
  

D. Enable Automatic Security Updates

For Debian/Ubuntu:

sudo apt install unattended-upgrades
sudo dpkg-reconfigure unattended-upgrades

For CentOS/RHEL:

sudo yum install yum-cron
sudo systemctl enable --now yum-cron

E. Secure File Permissions and Enable Logging

• Restrict access to system logs:

  sudo chmod -R 640 /var/log/
  sudo chown -R root:adm /var/log/
  

• Enable audit logging:

  sudo apt install auditd -y
  sudo systemctl enable auditd
  

  • Track root commands:

    sudo auditctl -w /etc/passwd -p wa -k passwd_changes
    

  • Review audit logs:

    sudo ausearch -k passwd_changes --start today
    

4. Schedule Regular Security Audits

To keep your system secure over time, automate periodic scans:

1. Run Lynis every Sunday at 3 AM:

   sudo crontab -e
   

   Add:

   0 3 * * 0 lynis audit system --quiet >> /var/log/lynis_cron.log
   

2. Send audit reports to administrators:

   mail -s "Weekly Linux Security Audit" admin@example.com < /var/log/lynis_cron.log
   

Best Practices for CIS Benchmark Implementation

✅ Use CIS-CAT or Lynis to automate security checks and compliance reports.
✅ Disable unnecessary services and restrict network access.
✅ Enforce strong authentication, least privilege, and secure file permissions.
✅ Automate security updates to patch vulnerabilities.
✅ Perform regular security audits and log monitoring.

By implementing CIS Benchmarks, you harden your Linux server against attacks, reduce misconfigurations, and ensure compliance with security standards.