If you are using Google Chrome on a Windows machine, it's time to pay attention. Google's Project Zero and the Chromium Projects security teams have unveiled an inappropriate implementation of fullscreen mode in Google Chrome on Windows, with versions prior to 132..6834.83. This security vulnerability is dubbed as CVE-2025-0440 and allows a remote attacker to perform UI spoofing by using a specially crafted HTML page.

In this post, we'll deep dive into the details of this vulnerability, offer insights into how attackers can exploit it, and share mitigation strategies to keep your systems safe. But first, here's a quick overview of the key terms involved in this vulnerability:

* UI Spoofing: A form of cyber-attack where an attacker creates a fake user interface (UI) to deceive users into entering sensitive information or performing unwanted actions.
* Fullscreen Mode: A feature present in web browsers which allows users to view content or media in full screen, usually by hiding or minimizing other UI elements.
* Chromium Project: Google's open-source web browser project on which the Chrome browser is based.

Now that we have these terms clear, let's dig deeper into the specifics of CVE-2025-0440.

Vulnerability Details

The Chromium security team has classified this vulnerability as "medium" in terms of severity. Let's look at a snippet of the code that shows this inappropriate implementation:

function enterFullScreen() {
  if (document.documentElement.requestFullscreen) {
    document.documentElement.requestFullscreen();
  } else if (document.documentElement.mozRequestFullScreen) { // Firefox
    document.documentElement.mozRequestFullScreen();
  } else if (document.documentElement.webkitRequestFullscreen) { // Chrome, Safari, and Opera
    document.documentElement.webkitRequestFullscreen();
  } else if (document.documentElement.msRequestFullscreen) { // IE/Edge
    document.documentElement.msRequestFullscreen();
  }
}

The above code is a simple JavaScript function that allows developers to request fullscreen mode using different browser-specific methods. We can see how the support for Chrome, Firefox, Safari, Opera, and Edge/IE are defined separately.

The vulnerability lies in the fact that the Google Chrome browser on Windows allows an attacker to manipulate fullscreen mode in an "inappropriate" way. Specifically, an attacker can create a specially crafted HTML page that, when viewed by a victim in fullscreen mode, appears legitimate but is in fact an entirely spoofed UI.

You can see how an attacker might use this to their advantage: by designing their false UI to closely resemble a trusted website, they could trick users into entering login credentials or personal information, all while the victim believes they are interacting with a legitimate site.

Exploitation of Vulnerability

The primary mode of exploitation for this vulnerability is phishing campaigns, where attackers send targeted email messages with links to the specially crafted HTML pages. Once a user falls for the attack and opens the malicious link in Chrome, the attacker initiates the UI spoofing attack by triggering the inappropriate fullscreen mode.

Here's a simple example of how an attacker might use this vulnerability

1. Attacker creates a fake "Bank ABC" login page that meticulously mimics the look and feel of the legitimate site.
2. Attacker sends a phishing email to potential victims, claiming to be from Bank ABC, and asking users to click on a link to verify their account details.

Victim clicks the link, opening the fake Bank ABC login page in Google Chrome on Windows.

4. The page initiates the fullscreen mode with the inappropriate implementation, causing the fake UI to appear legitimate.

Mitigation Strategies

Google has addressed the vulnerability in Chrome version 132..6834.83. Users are advised to update their browser immediately to protect themselves against this security flaw.

Other general security measures to protect against phishing attacks and similar vulnerabilities include:

1. Ensure your operating system, browser, and all software are up-to-date with the latest security patches.
2. Avoid clicking on links in unsolicited emails, particularly those requesting personal information or login details.
3. Verify the authenticity of websites before inputting sensitive information, by checking for HTTPS and the green padlock symbol in the browser's address bar.
4. Use strong, unique passwords for all your accounts, and consider using a password manager to help manage them.

Conclusion

CVE-2025-0440 is a medium-severity vulnerability that demonstrates the importance of staying vigilant against potential UI spoofing attacks. By keeping your software updated and following best-practice security measures, you can minimize your risk of falling victim to a similar exploitations. Stay safe!

Original References

* Google Chrome Release Blog Post
* CVE-2025-0440: Chromium Vulnerability
* Google's Project Zero

Timeline

Published on: 01/15/2025 11:15:10 UTC
Last modified on: 01/15/2025 15:15:15 UTC