In this post, we will discuss and analyze the CVE-2023-4579 vulnerability found in Firefox versions prior to 117. This vulnerability allowed search queries in the default search engine to appear as the currently navigated URL if the search query was a well-formed URL. Consequently, this could lead to a site spoofing another if it had been maliciously set as the default search engine.

We will dive deep into how this vulnerability works, provide a code snippet highlighting the issue, and elaborate on how to exploit it. Before we begin, let's explore the original references related to this vulnerability.

Original References

1. Mozilla Foundation Security Advisory:
2. CVE Details Page:

Exploit Details

The flaw exists in the handling of search queries in the default search engine by the Firefox browser. If an attacker can set a malicious website as the default search engine, they can craft a search query that is actually a well-formed URL. By doing so, the browser will display this URL in the address bar, deceiving the user into believing it is the actual navigated website.

Set a malicious website as the default search engine in the victim's Firefox browser.

2. Pick a target website that the attacker wants to spoof (e.g., '').

Entice the victim to perform a search using the malicious search engine.

If the victim falls for the trick and performs a search, the address bar in Firefox will display the attacker's crafted URL, giving the impression of visiting the target website. This way, the attacker can launch phishing attacks and steal sensitive data from the victim.

Here is a simplified code snippet demonstrating the flaw in the Firefox browser

// Malicious search engine URL
const maliciousSearchEngine = "";;

// Victim's search query (that is actually a well-formed URL mimicking a target website)
const searchQuery = "";

// Firefox handling the search query
navigateTo(maliciousSearchEngine + searchQuery);

 * The address bar will show:
 * Instead of the actual navigated URL.


The only way to protect yourself from this vulnerability is by updating to Firefox version 117 or later. Mozilla has fixed the issue in this version, and it is essential to keep your browser up-to-date with the latest security patches.


CVE-2023-4579 is an interesting vulnerability that highlights the importance of proper URL handling and the potential risks of default search engine manipulation.

To ensure your online safety, it is crucial to maintain an updated browser and be cautious of any strange search results or unexpected changes in your default search engine. Additionally, always be vigilant and skeptical about the websites you visit and take necessary precautions such as enabling multi-factor authentication and using strong passwords.


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