In this long-read post, we delve into the details of CVE-2023-25730, a security vulnerability that affects multiple Mozilla products, including Firefox, Thunderbird, and Firefox ESR. By taking advantage of this flaw, an attacker can potentially confuse users or launch spoofing attacks. We will discuss the background, impact, and affected versions, plus share some code snippets and references to help you understand and mitigate this vulnerability.


The core of CVE-2023-25730 lies in the 'requestFullscreen' function, which allows a web application to enter fullscreen mode. When a background script calls for this function and then intentionally blocks the main browser thread, it can force the browser into fullscreen mode indefinitely. This could result in potential user confusion or spoofing attacks if attackers manage to create a fake version of a legitimate website, tricking users into revealing sensitive information.

Here's a sample code snippet that demonstrates the vulnerability

async function exploit() {
  // Request fullscreen
  const targetElement = document.documentElement;

  // Block the main thread
  while (true) {
    await new Promise(resolve => setTimeout(resolve, 100));


The code above requests fullscreen mode for the <html> element and then blocks the main thread by repeatedly waiting without ever releasing control. The browser would be stuck in fullscreen mode as long as the page remains open, leaving the user vulnerable to spoofing attacks.

Exploit Details

To exploit this vulnerability, an attacker would need to create a malicious website or inject the malicious code into a legitimate website through a separate vulnerability. When users visit the compromised site, the browser would be forced into fullscreen mode without the user's explicit permission.

Next, the attacker could recreate the legitimate website's interface inside the fullscreen mode, prompting the user to enter sensitive information such as login credentials or personal information. Since the browser window is stuck in fullscreen mode, the user might not notice the difference between the real website and the fake one, making it easier for the attacker to collect sensitive data.

Mitigation and Recommendations

To protect yourself from this vulnerability, ensure that you are running the latest versions of the affected Mozilla products. If you are using Firefox, Thunderbird, or Firefox ESR, make sure to update them to the following versions or later:

Firefox ESR 102.8

Additionally, be cautious when visiting unfamiliar websites and look for signs of spoofing, such as incorrect URLs or missing security indicators.

Original References

For more information on CVE-2023-25730 and other related vulnerabilities, please visit the following links:

1. CVE-2023-25730 | MITRE CVE Entry
2. Mozilla Foundation Security Advisory 2023-04


CVE-2023-25730 serves as a timely reminder for users to keep their software up to date and remain vigilant against potential spoofing attacks. By understanding the issue and its implications, you can take preventive steps to safeguard your online security and ensure a safe browsing experience.


Published on: 06/02/2023 17:15:00 UTC
Last modified on: 06/08/2023 17:16:00 UTC