---

When we talk about online safety, browsers are your biggest frontline defense. But what if that shield has a crack? That’s exactly what CVE-2023-21794 is – a serious spoofing vulnerability found in Microsoft Edge (Chromium-based). In this long read, I’ll explain what this vulnerability is, how attackers could exploit it, share some sample code, and give you the best resources available. Whether you are a developer, IT specialist, or just a curious user, you’ll get all you need to know in everyday language.

What Is CVE-2023-21794?

CVE-2023-21794 affects Microsoft Edge, a browser that’s built on Chromium (the same engine used by Google Chrome). This is not just about a random error or crash; it’s a “spoofing” vulnerability. That means an attacker could trick you into thinking you’re looking at one thing, when you’re really seeing something else—like a fake login page.

Spoofing vulnerabilities are dangerous: They let a bad actor present misleading information to users. For a browser, this could mean faking the URL bar, security indicators, or parts of the page to steal personal data or login credentials.

> A spoofing vulnerability exists when Microsoft Edge (Chromium-based) fails to properly handle specific URLs, potentially allowing an attacker to obscure the actual address of a loaded website.

Reference

- Microsoft CVE-2023-21794 Security Update Guide

Technical Details: How Does the Exploit Work?

The core of this vulnerability is in how Microsoft Edge parsed and displayed certain specially crafted URLs. An attacker can manipulate the way URLs are handled, so the browser’s address bar shows a trusted domain, while actually loading content from another, malicious location.

The Process in Simple Terms

1. Craft Special URL: The attacker creates a URL using control characters or special schemes that Edge mishandles.

3. Deceptive Address Bar: When the link is clicked, the page opens in Microsoft Edge. The address bar appears to display a trusted website (like https://login.microsoft.com), but the page is actually a spoofed site controlled by the attacker.
4. Steal Information: Users may enter their passwords or confidential data, thinking the site is genuine.

Demonstration Code Snippet

Let’s walk through a basic “proof-of-concept” (PoC) approach similar to those used by security researchers. Don’t use this for harm—it’s for education only!

Suppose Edge doesn’t properly sanitize Unicode right-to-left override (RTLO) characters in URLs. Attackers might use this to swap parts of a URL visually.

<!-- Phishing page with RTLO -->
<!DOCTYPE html>
<html>
  <head>
    <title>Microsoft Edge Spoofing PoC</title>
  </head>
  <body>
    <a href="http://evil.com/%E2%80%AEten.retnecliam%2Fmoc.elgoog//:sptth">Click here to log in with your Microsoft account</a>
  </body>
</html>

%E2%80%AE is the Unicode for RTLO (U+202E).

- When Edge does not handle this correctly, the URL behind the link in the address bar could look like https://google.com/microsoft.net (visually), while the browser is actually loading from evil.com.

Important: Real-world attacks can combine many tricks, including embedded iframes, HTML/CSS disguising, and more.

Real-World Impact

If you’re a user, that means even if you look at the address bar and think you’re safe, you might not be. For organizations, this type of vulnerability is a goldmine for phishers aiming to steal company credentials.

References and Further Reading

- Microsoft Security Advisory
- NVD - CVE-2023-21794
- Chromium Security Documentation
- Example research on URL Spoofing: PortSwigger - URL Spoofing

Final Thoughts

CVE-2023-21794 is a classic reminder: even trusted browsers can have blind spots. Stay updated, be cautious with links, and remember that what you see in the address bar isn’t always the full story. Tech moves fast – keep your browser faster (and patched)!


*Feel free to share this post with your team or anyone who needs an easy, clear guide on the dangers behind Microsoft Edge spoofing vulnerabilities like CVE-2023-21794.*

Timeline

Published on: 02/14/2023 20:15:00 UTC
Last modified on: 02/23/2023 16:07:00 UTC