CVE-2020-36867
📋 TL;DR
This vulnerability allows authenticated attackers in Nagios XI to execute arbitrary commands on the server by injecting shell metacharacters into PDF report generation parameters. Attackers can achieve remote code execution with the privileges of the Nagios XI process. All Nagios XI installations prior to version 5.7.3 are affected.
💻 Affected Systems
- Nagios XI
📦 What is this software?
Nagios Xi by Nagios
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise allowing attackers to execute arbitrary commands as the Nagios XI process user, potentially leading to lateral movement, data exfiltration, or complete server takeover.
Likely Case
Authenticated attackers with report generation privileges gain remote code execution, potentially installing backdoors, stealing monitoring data, or pivoting to other systems.
If Mitigated
With proper network segmentation and least privilege access, impact is limited to the Nagios XI server itself without lateral movement capabilities.
🎯 Exploit Status
Exploitation requires authenticated access but is straightforward once authenticated. Public exploit code exists.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.7.3
Vendor Advisory: https://www.nagios.com/changelog/nagios-xi/
Restart Required: Yes
Instructions:
1. Backup current Nagios XI configuration and data. 2. Download Nagios XI 5.7.3 or later from the Nagios website. 3. Follow the official upgrade instructions at https://assets.nagios.com/downloads/nagiosxi/docs/Upgrading-Nagios-XI.pdf. 4. Restart Nagios XI services after upgrade.
🔧 Temporary Workarounds
Disable PDF report generation
linuxTemporarily disable PDF report generation functionality to prevent exploitation while planning upgrade.
# Remove or restrict access to PDF generation scripts
# Example: chmod 000 /usr/local/nagiosxi/html/includes/components/pdf/*
Restrict user permissions
allLimit which users have permissions to generate PDF reports to only essential personnel.
# Review and modify user permissions in Nagios XI Admin > Users
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Nagios XI from critical systems
- Deploy application-level firewall rules to block suspicious PDF generation requests
🔍 How to Verify
Check if Vulnerable:
Check Nagios XI version via Admin > About in web interface or run: cat /usr/local/nagiosxi/var/xiversionCheck Version:
cat /usr/local/nagiosxi/var/xiversionVerify Fix Applied:
Verify version is 5.7.3 or higher and test PDF report generation functionality works without errors.📡 Detection & Monitoring
Log Indicators:
- Unusual PDF generation requests with special characters in parameters
- Suspicious command execution in Nagios XI process logs
- Multiple failed PDF generation attempts
Network Indicators:
- Unusual outbound connections from Nagios XI server
- PDF generation requests containing shell metacharacters
SIEM Query:
source="nagios_xi" AND (event="pdf_generation" AND (param="*;*" OR param="*|*" OR param="*`*" OR param="*$(*"))