CVE-2025-0246 - How an Invalid Protocol Scheme on Android Firefox Lets Hackers Fake The Address Bar

CVE-2025-0246 is a serious vulnerability found in versions of Firefox for Android before version 134. This bug allowed an attacker to *spoof*—or fake—the address bar in a way that tricks users into thinking they're on a trusted website when they're really looking at a malicious one.

Note:

Why Does This Matter?

The address bar at the top of your browser tells you what site you’re visiting—like https://www.bank.com. If a hacker can fake this bar, they can trick you into entering your passwords, credit card information, or personal data. If you're using Firefox < 134 on Android, you could be at risk.

How Does The Bug Work?

At a basic level, Firefox for Android didn’t properly handle URLs ("Uniform Resource Locators") with invalid or strange protocol schemes in special situations. A protocol scheme is just the first part of a URL, like http:// or ftp://.

Attackers found that if they crafted a specially malformed URL and convinced someone to click it (maybe via an email, SMS, or a malicious web page), Firefox could get confused. It would display a legitimate-looking website name in the address bar—even though the real content was coming from a malicious site.

`

fakebank://@realbank.com#attackersite.com

`

Firefox Displays Tricked Address Bar

Due to the bug, Firefox might show realbank.com in the address bar, though the user is actually on attackersite.com.

Attacker Serves Phishing Page

The page asks for passwords, login info, or personal data, and the user is unaware because the address bar *looks* real.

Here's a simple example you could experiment with (only for educational testing!)

<!-- Save as test.html and open with Firefox for Android < 134 -->
<a href="invalid://@paypal.com#evilsite.com">Tap me - Exclusive offer!</a>

If the bug is present, Firefox may begin to load the link. During or after this, the address bar can be confused and display paypal.com or some of its fragment, even though you *never* left the attacker's website.

> ⚠️ Never use this in a real attack or outside of safe, isolated environments.

Technical Details

This bug basically lets the attacker insert a @ symbol and a fragment (#) in a way that separates the real origin and the spoofed display:

The # can sometimes trick the browser into loading attacker-supplied content.

The vulnerable Firefox versions missed a proper check for these malformed URLs, especially with *custom* or *unknown* schemes.

Below, a simple proof-of-concept JavaScript will launch a fake URL and open a spoofed page

<!DOCTYPE html>
<html>
  <body>
    <button onclick="window.location.href = 'fake://@example.com#evilsite.com'">
      Click here for an amazing deal!
    </button>
  </body>
</html>

On tap in a buggy Android Firefox, the address bar may misrepresent your actual location.

- Bugzilla entry for CVE-2025-0246 (Mozilla Bug Tracker) *(replace with actual bug number when available)*
- Mozilla Security Advisory *(refer to advisory for CVE-2025-0246)*
- Phishing With Mobile Browsers: Google Research Blog *(Background about address bar spoofing)*
- Mitre CVE Database

Conclusion

CVE-2025-0246 is a reminder that even trusted browser features can be misused if tiny parsing bugs slip through. Mobile users especially are at risk because the address bar is the last visual clue to what you’re visiting.

Always keep your apps updated—and if you’re running Firefox for Android before version 134, update it right now.

Stay safe—and always check your address bar!

*For bug report links and more examples, refer to the official Mozilla Security Advisory or CVE entry above.*

Timeline

Published on: 01/07/2025 16:15:39 UTC
Last modified on: 01/08/2025 16:15:37 UTC