CVE-2020-15903
📋 TL;DR
CVE-2020-15903 is a privilege escalation vulnerability in Nagios XI where backend scripts running as root included files editable by the lower-privileged nagios user. This allows the nagios user to escalate to root privileges by modifying these files. All Nagios XI installations before 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 with root access, allowing attackers to install persistent backdoors, exfiltrate sensitive data, or pivot to other systems.
Likely Case
Privilege escalation from nagios user to root, enabling complete control over the Nagios XI system and potentially adjacent systems.
If Mitigated
Limited impact if proper access controls and monitoring are in place, though privilege escalation remains possible.
🎯 Exploit Status
Exploitation requires existing access as nagios user, but the privilege escalation mechanism is straightforward once authenticated.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.7.3
Vendor Advisory: https://www.nagios.com/downloads/nagios-xi/change-log/
Restart Required: Yes
Instructions:
1. Backup current Nagios XI configuration. 2. Download Nagios XI 5.7.3 or later from Nagios website. 3. Follow the official upgrade instructions. 4. Restart Nagios XI services.
🔧 Temporary Workarounds
Restrict file permissions
linuxRemove write permissions for nagios user on critical backend script files
find /usr/local/nagiosxi -type f -name '*.php' -exec chmod o-w {} \;
find /usr/local/nagiosxi -type f -name '*.inc' -exec chmod o-w {} \;
🧯 If You Can't Patch
- Restrict access to Nagios XI interface to trusted networks only
- Implement strict monitoring of file modifications in Nagios XI directories
🔍 How to Verify
Check if Vulnerable:
Check Nagios XI version: if version is less than 5.7.3, system is vulnerableCheck Version:
grep 'version' /usr/local/nagiosxi/var/xiversionVerify Fix Applied:
Verify version is 5.7.3 or higher and check file permissions on backend scripts📡 Detection & Monitoring
Log Indicators:
- Unexpected file modifications in /usr/local/nagiosxi directories
- Unusual privilege escalation attempts from nagios user
Network Indicators:
- Unusual outbound connections from Nagios XI server
SIEM Query:
source="nagios" AND (event_type="file_modification" OR user="nagios" AND privilege="root")