Use a Host-Based Intrusion Detection System (HIDS)

A Host-Based Intrusion Detection System (HIDS) continuously monitors system logs, file integrity, user activity, and network behavior to detect suspicious activity. If an attacker compromises your server, HIDS can:

✅ Detect unauthorized file modifications or privilege escalation attempts.
✅ Alert you in real-time about potential intrusions or security violations.
✅ Provide forensic logs for investigating security incidents.

HIDS solutions such as OSSEC, Wazuh, and Tripwire help identify anomalies and prevent security breaches.

How to Install and Configure OSSEC (HIDS) on Your Linux Server

1. Install OSSEC HIDS

For Debian/Ubuntu:

sudo apt install ossec-hids -y

For CentOS/RHEL:

sudo yum install ossec-hids -y

2. Configure OSSEC to Monitor System Activity

1. Edit the OSSEC configuration file:

   sudo nano /var/ossec/etc/ossec.conf
   

2. Define monitoring rules (e.g., log files, directories, SSH activity). Example:

   <localfile>
       <log_format>syslog</log_format>
       <location>/var/log/auth.log</location>
   </localfile>
   

   (Monitors /var/log/auth.log for suspicious SSH logins.)

3. Save and close the file.

3. Enable OSSEC Alerting

1. Set up email alerts for security events:

   <global>
       <email_notification>yes</email_notification>
       <email_to>admin@example.com</email_to>
       <smtp_server>smtp.example.com</smtp_server>
   </global>
   

   (Replace admin@example.com with your email.)

2. Restart OSSEC to apply changes:

   sudo systemctl restart ossec
   

4. Verify OSSEC is Running Properly

• Check OSSEC status:

  sudo systemctl status ossec
  

• View real-time alerts:

  sudo cat /var/ossec/logs/alerts.log
  

Alternative: Install Wazuh (Advanced OSSEC-Based HIDS)

Wazuh is an enhanced fork of OSSEC with a web dashboard, SIEM integration, and advanced threat detection.

1. Install Wazuh on Debian/Ubuntu:

   curl -sO https://packages.wazuh.com/4.x/wazuh-install.sh
   sudo bash wazuh-install.sh --wazuh-server
   

2. Enable Wazuh monitoring:

   sudo systemctl start wazuh-manager
   

Best Practices for HIDS Security

✅ Monitor system logs (/var/log/auth.log, /var/log/syslog) for unusual activity.
✅ Enable real-time alerting to receive security notifications immediately.
✅ Integrate HIDS with a SIEM (e.g., ELK, Splunk, or Graylog) for central log analysis.
✅ Regularly update detection rules to stay protected against evolving threats.

By deploying HIDS solutions like OSSEC or Wazuh, you can detect security threats early, prevent system compromises, and maintain a well-monitored Linux server.