CVE-2019-15949

Nagios XI is used to monitor servers and services. This flaw lets an attacker—if they can reach certain Nagios XI access paths—replace a plugin/check and turn that monitoring feature into a way to run commands as the system’s highest-privilege user (root). Think of it like swapping out a trusted tool the monitoring system relies on so it becomes a “back door” instead.

This matters if you run Nagios XI and your installation is older than 5.6.6. The exploit is not just “scan-and-crack” for random internet users; it needs access to the server as the nagios user or access as the admin user via the web interface. Because of that, it’s mainly a risk when an attacker can already reach those accounts or permissions (for example through compromised credentials or an insider account).

This is RED because confirmed real-world exploitation has been added to CISA’s Known Exploited Vulnerabilities list. If an attacker gains the required access path (nagios user or Nagios XI admin via the web interface), they can run arbitrary commands as root, leading to full server compromise. Treat upgrading as an immediate priority, not a routine maintenance item.

1. Confirm exposure (version)

   • Log into Nagios XI and check the installed version.
   • If the version is earlier than 5.6.6, you are affected.

2. Confirm exposure (access paths)

   • Determine who has (a) the ability to modify plugins/checks via Nagios XI and (b) Nagios XI admin web access.
   • Review recent authentication events to see whether the nagios user or Nagios XI admin account was accessed unexpectedly.

3. Upgrade to the fixed version

   • Upgrade Nagios XI to 5.6.6 or later.
   • During/after the upgrade, validate that plugin/check files and scripts were not modified in the meantime.

4. If patching is delayed (temporary containment)

   • Immediately reduce who can access the Nagios XI admin interface and who can modify plugins/checks.
   • If feasible, revoke or rotate credentials for any accounts that have admin or plugin-modification privileges.
   • Review the server for evidence of malicious changes to check/plugin executables (unexpected new content, timestamps that don’t match your change window, or altered permissions).

5. After upgrade: verify and watch

   • Re-check the Nagios XI version is now 5.6.6+.
   • Look for unexpected executions tied to the plugin/check mechanism and investigate any abnormal process activity originating from the monitoring components.

Severity is high (capable of executing arbitrary code as root). The weakness is in Nagios XI’s handling of data passed into a root-executed script (CWE-78). The attack vector is network-triggered execution through the Nagios XI profile download flow (profile.php?cmd=download → getprofile.sh), where the script ends up running a plugin/check component with elevated privileges; by modifying the plugin/check executable (under the nagios user’s control), an attacker can cause arbitrary command execution as root.

KEV status: This CVE is listed in CISA KEV (added 2021-11-03), meaning it has been observed in the wild and tracked for remediation; CISA’s remediation due date was 2022-05-03.

Exploitation maturity: Public proof-of-concept exists, and exploitation is confirmed via KEV listing.

Fix: Nagios XI is fixed in 5.6.6.