CVE-2020-28901
📋 TL;DR
CVE-2020-28901 is a command injection vulnerability in Nagios Fusion that allows attackers to execute arbitrary commands with root privileges. The vulnerability exists in the cmd_subsys.php component and affects Nagios Fusion 4.1.8 and earlier versions. Attackers can exploit this to gain complete control of affected systems.
💻 Affected Systems
- Nagios Fusion
📦 What is this software?
Fusion by Nagios
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with root-level code execution, allowing attackers to install persistent backdoors, exfiltrate sensitive data, or pivot to other systems in the network.
Likely Case
Privilege escalation leading to complete system takeover, enabling attackers to manipulate monitoring data, disable alerts, or use the compromised system as a foothold for lateral movement.
If Mitigated
Limited impact if proper network segmentation, least privilege principles, and command injection protections are implemented, though the vulnerability still presents significant risk.
🎯 Exploit Status
Exploitation requires some level of access to the system, but the vulnerability is well-documented with public proof-of-concept code available. The command injection is straightforward once the vulnerable component is reached.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Nagios Fusion 4.1.9 and later
Vendor Advisory: https://www.nagios.com/downloads/nagios-xi/change-log/
Restart Required: Yes
Instructions:
1. Backup current configuration and data. 2. Download Nagios Fusion 4.1.9 or later from the official Nagios website. 3. Follow the upgrade instructions in the Nagios documentation. 4. Restart Nagios Fusion services. 5. Verify the upgrade was successful.
🔧 Temporary Workarounds
Restrict access to cmd_subsys.php
linuxTemporarily block or restrict access to the vulnerable cmd_subsys.php file while awaiting patching.
sudo chmod 000 /usr/local/nagiosfusion/html/includes/cmd_subsys.php
sudo mv /usr/local/nagiosfusion/html/includes/cmd_subsys.php /usr/local/nagiosfusion/html/includes/cmd_subsys.php.disabled
Implement web application firewall rules
allConfigure WAF rules to block suspicious patterns in requests to cmd_subsys.php.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Nagios Fusion from critical systems
- Apply principle of least privilege and monitor for unusual root-level activity
🔍 How to Verify
Check if Vulnerable:
Check Nagios Fusion version: cat /usr/local/nagiosfusion/var/product_version.txt. If version is 4.1.8 or earlier, the system is vulnerable.Check Version:
cat /usr/local/nagiosfusion/var/product_version.txtVerify Fix Applied:
Verify version is 4.1.9 or later: cat /usr/local/nagiosfusion/var/product_version.txt. Also check that cmd_subsys.php has been properly patched or restricted.📡 Detection & Monitoring
Log Indicators:
- Unusual commands executed via PHP processes
- Access to cmd_subsys.php with suspicious parameters
- Root privilege escalation attempts in system logs
Network Indicators:
- Unexpected outbound connections from Nagios Fusion system
- Suspicious HTTP requests to cmd_subsys.php endpoint
SIEM Query:
source="nagios_fusion_logs" AND (uri="*cmd_subsys.php*" AND (param="*;*" OR param="*|*" OR param="*`*"))🔗 References
- http://packetstormsecurity.com/files/162783/Nagios-XI-Fusion-Privilege-Escalation-Cross-Site-Scripting-Code-Execution.html
- https://skylightcyber.com/2021/05/20/13-nagios-vulnerabilities-7-will-shock-you/
- https://www.nagios.com/downloads/nagios-xi/change-log/
- http://packetstormsecurity.com/files/162783/Nagios-XI-Fusion-Privilege-Escalation-Cross-Site-Scripting-Code-Execution.html
- https://skylightcyber.com/2021/05/20/13-nagios-vulnerabilities-7-will-shock-you/
- https://www.nagios.com/downloads/nagios-xi/change-log/
