1. Introduction
Nagios XI 5.7.5 suffers from a command injection vulnerability in several web application components. This allows an attacker with authenticated access to execute arbitrary commands on the server, potentially compromising system confidentiality, integrity and availability. Systems running Nagios XI 5.7.5 are affected. Impact is likely to be high due to potential for complete system takeover.
2. Technical Explanation
The vulnerability stems from insufficient sanitisation of user-supplied input in the /usr/local/nagiosxi/html/includes/configwizards directories. Specifically, files windowswmi.inc.php, switch.inc.php and cloud-vm.inc.php are affected (CVEs 2021-25296, 2021-25297, and 2021-25298 respectively). An attacker can inject commands into HTTP requests processed by these files.
- Root cause: Improper sanitization of authenticated user-controlled input within the specified PHP files allows for command execution.
- Exploit mechanism: An attacker sends a crafted HTTP request containing malicious code that is then executed as a system command on the server. For example, an attacker could inject a command to create a new user account or download malware.
- Scope: Nagios XI 5.7.5 is affected. Other versions may also be vulnerable; check vendor advisories.
3. Detection and Assessment
Confirming vulnerability requires checking the installed version of Nagios XI, then verifying input sanitisation.
- Quick checks: Check the Nagios XI web interface for the version number (usually in the ‘About’ section).
- Scanning: Nessus plugin ID 163458 may identify this vulnerability, but relies on self-reported version information.
- Logs and evidence: Review application logs for suspicious activity related to command execution attempts. Look for unusual processes spawned by the Nagios XI user.
# Check Nagios XI version (example - actual path may vary)
cat /usr/local/nagiosxi/html/about.php | grep "Version"
4. Solution / Remediation Steps
Apply the vendor-supplied patch or upgrade to a fixed version of Nagios XI.
4.1 Preparation
- Ensure you have access to the Nagios XI web interface and command line. A roll back plan involves restoring the backed-up configuration files and restarting the service.
- A change window may be required, depending on your environment’s policies. Approval from a senior administrator is recommended.
4.2 Implementation
- Step 1: Download the latest Nagios XI update package from the official Nagios website.
- Step 2: Apply the patch or upgrade using the Nagios XI web interface (Admin > Updates).
4.3 Config or Code Example
Before
#Example - Actual code will vary, this is illustrative only
$command = $_REQUEST['cmd'];
exec($command);
After
#Example - Actual code will vary, this is illustrative only
$command = escapeshellarg($_REQUEST['cmd']);
exec($command);
4.4 Security Practices Relevant to This Vulnerability
Several security practices can help prevent command injection vulnerabilities.
- Practice 2: Least privilege reduces the impact of a successful exploit by limiting what an attacker can do on the system.
4.5 Automation (Optional)
#Example - This is illustrative only and may not be applicable to Nagios XI
#!/bin/bash
# Stop Nagios XI service
systemctl stop nagiosxi
# Apply patch (replace with actual command)
yum update nagiosxi
# Start Nagios XI service
systemctl start nagiosxi
5. Verification / Validation
Confirm the fix by checking the updated version and attempting a test injection.
- Post-fix check: Check the Nagios XI web interface for the updated version number.
- Re-test: Attempt to inject a command through the affected interfaces (windowswmi, switch, cloud-vm) and verify that it does not execute.
- Smoke test: Verify core Nagios XI functionality such as host monitoring and alerting still works correctly.
# Check Nagios XI version (example - actual path may vary)
cat /usr/local/nagiosxi/html/about.php | grep "Version"
#Expected output should show updated version number
6. Preventive Measures and Monitoring
Update security baselines to include the latest Nagios XI patch level.
- Baselines: Update your security baseline or policy to require regular patching of Nagios XI.
- Pipelines: Consider using static application security testing (SAST) tools to identify potential input validation issues during development.
- Asset and patch process: Implement a regular patch review cycle for all critical systems, including Nagios XI.
7. Risks, Side Effects, and Roll Back
Applying the patch may cause temporary service disruption.
- Risk or side effect 1: Patching could temporarily interrupt monitoring services. Schedule during a maintenance window.
- Roll back: Restore the backed-up Nagios XI configuration directory and restart the service if patching fails.
8. References and Resources
- Vendor advisory or bulletin: https://www.nagios.com/downloads/nagios-xi/change-log/
- NVD or CVE entry: CVE-2021-25296, CVE-2021-25297, CVE-2021-25298
- Product or platform documentation relevant to the fix: https://www.nagios.com/products/security/