CVE-2020-36856
📋 TL;DR
This vulnerability allows authenticated users with Core Config Manager access in Nagios XI to execute arbitrary commands on the host system by injecting shell metacharacters into the address parameter of the command_test.php script. Attackers can leverage this to compromise the Nagios XI host, modify configurations, or gain full system control. Organizations running Nagios XI versions before 5.6.14 are affected.
💻 Affected Systems
- Nagios XI
📦 What is this software?
Nagios Xi by Nagios
⚠️ Risk & Real-World Impact
Worst Case
Full compromise of the Nagios XI host leading to lateral movement within the network, data exfiltration, or deployment of persistent malware/ransomware.
Likely Case
Authenticated attackers with legitimate or stolen credentials execute commands to escalate privileges, modify monitoring configurations, or establish backdoors.
If Mitigated
Limited impact due to network segmentation, strict access controls, and monitoring that detects unusual command execution patterns.
🎯 Exploit Status
Exploitation requires valid authentication credentials. Multiple public proof-of-concept exploits exist demonstrating command injection.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.6.14 and later
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 5.6.14 or later from Nagios customer portal. 3. Follow official upgrade instructions at https://assets.nagios.com/downloads/nagiosxi/docs/Upgrading-Nagios-XI.pdf. 4. Verify upgrade completed successfully and test monitoring functionality.
🔧 Temporary Workarounds
Disable CCM Access
allTemporarily restrict or disable Core Config Manager access for non-administrative users
# Modify user permissions in Nagios XI admin interface to remove CCM access
# Or disable CCM component entirely if not required
Web Application Firewall Rules
allImplement WAF rules to block requests containing shell metacharacters in address parameter
# Example ModSecurity rule: SecRule ARGS:address "[;|&`$()]" "id:1001,phase:2,deny,status:403,msg:'Command injection attempt'"
# Adjust for your specific WAF platform
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Nagios XI from critical systems
- Enforce multi-factor authentication and review all user accounts with CCM access
🔍 How to Verify
Check if Vulnerable:
Check Nagios XI version via Admin > System Config > About or run: grep 'fullversion' /usr/local/nagiosxi/html/config.inc.phpCheck Version:
grep 'fullversion' /usr/local/nagiosxi/html/config.inc.php | cut -d"'" -f2Verify Fix Applied:
Verify version is 5.6.14 or higher and test that command_test.php script properly validates address parameter input📡 Detection & Monitoring
Log Indicators:
- Unusual command execution patterns in Nagios XI logs
- Multiple failed authentication attempts followed by successful login and CCM access
- Web server logs showing POST requests to command_test.php with shell metacharacters in parameters
Network Indicators:
- Outbound connections from Nagios XI server to unexpected destinations
- Unusual network traffic patterns following successful authentication
SIEM Query:
source="nagios_xi_logs" AND (uri_path="*command_test.php*" AND (param="*;*" OR param="*|*" OR param="*`*" OR param="*$(*"))