CVE-2024-26465 - Critical DOM-based XSS in stewdio beep.js (Before commit ef22ad7) Explained with Exploit Details

CVE-2024-26465 is a DOM-based Cross-Site Scripting (XSS) vulnerability detected in the /beep/Beep.Instrument.js component of stewdio beep.js, a popular JavaScript library for audio synthesis and music creation in the browser. Versions before commit ef22ad7 are affected.

This vulnerability allows attackers to execute arbitrary JavaScript in the context of the user’s browser by tricking them into visiting a specially crafted URL. This means your music app, sound demo, or learning project using beep.js could be used as a launching pad for further attacks, like session hijacking or phishing.

In this post, we’ll break down how the flaw works, what led to it, and how a real exploit looks—including code snippets you can recognize and avoid.

What is DOM-based XSS?

DOM-based XSS occurs when the JavaScript in your page directly takes user input (from things like the URL, form fields, or cookies) and injects it into the DOM (the page’s live code) without sanitizing it. Instead of the server, the browser itself creates the XSS hole.

Where’s the Bug in Beep.js?

The relevant code is in Beep.Instrument.js. In vulnerable versions, the library took a value (let’s say instrument options or parameters) from the URL, and inserted it directly into the page without proper escaping or validation.

Let’s take a simplified version of what happened. Imagine the webpage does something like this

// Inside Beep.Instrument.js, before commit ef22ad7
var params = new URLSearchParams(window.location.search);
var instrument = params.get('instrument') || 'piano';

// Directly inserting potentially malicious value into the page or a script
document.getElementById('output').innerHTML = "Selected: " + instrument;

If an attacker crafts a malicious URL like

https://victimsite.com/demo.html?instrument=<img src=x onerror=alert('XSS')>

The innerHTML assignment will insert an <img> tag with an onerror event, leading to the execution of arbitrary JavaScript.

Exploit Demonstration

Let’s see how an attacker could exploit this vulnerability.

`

https://vulnerablesite.com/demo.html?instrument=

Victim clicks the link, and the vulnerable code on the site does

var params = new URLSearchParams(window.location.search);
var instrument = params.get('instrument') || 'piano';
document.getElementById('output').innerHTML = "Selected: " + instrument;

Which becomes

<div id="output">
  Selected: <img src=x onerror=alert('Hacked by XSS')>
</div>

So the browser pops up a JavaScript alert, but a real-world attacker could steal cookies or act on behalf of the user.

Responsible Disclosure & Patch

The vulnerability was addressed in commit ef22ad7. The fix involves sanitizing user-submitted data and never inserting it as raw HTML.

Secure Code Example

// Sanitizing by assigning as text, not HTML
document.getElementById('output').textContent = "Selected: " + instrument;

Or, if you need to sanitize HTML, use a library like DOMPurify.

Mitigation Steps

- Upgrade beep.js to the latest version after commit ef22ad7.

More Resources

- NVD CVE-2024-26465 Entry (will be updated as details go public)
- beep.js GitHub Repository
- Commit ef22ad7 - Fix Details
- OWASP XSS Prevention Cheat Sheet: https://owasp.org/www-community/xss-prevention

Conclusion

CVE-2024-26465 demonstrates how easy it is for a DOM-based XSS vulnerability to slip into even music or audio libraries like beep.js. If your project uses beep.js, update now. Always sanitize user input, and think carefully before putting any user data into your page’s HTML.

Timeline

Published on: 02/26/2024 16:27:59 UTC
Last modified on: 11/25/2024 19:15:08 UTC