In September 2023, Microsoft addressed several security vulnerabilities in their products with the monthly Patch Tuesday cycle. One of these, tracked as CVE-2023-36727, affected the Chromium-based Microsoft Edge browser. This vulnerability was classified as a Spoofing Vulnerability, meaning an attacker could trick a user into believing what they saw in the browser was genuine—when in fact, it was not.

This post explores what CVE-2023-36727 is, how attackers could exploit it, what the developers did to fix it, and simple code and demo to show you how spoofing vulnerabilities work.

1. What is CVE-2023-36727?

CVE-2023-36727 is a security flaw in how Microsoft Edge presents web content. Because of a weakness in Edge’s Chromium engine, crafty attackers could make a webpage show a fake address in the browser's address bar, or fake other browser user interface elements.

This could trick you into giving away passwords, downloading malware, or believing you're on a website you actually are not.

2. How Does Spoofing via Edge Work?

Spoofing vulnerabilities generally work by breaking the trust between the browser’s UI and the actual web content. For CVE-2023-36727, the details reveal the flaw involves malicious JavaScript combined with creative use of HTML and window management.

For example, an attacker could use window.open combined with CSS and JavaScript redirects to control the appearance of the tab or address bar.

3. Example Code Snippet: How a Spoof Might Happen

Below is a simplified demonstration—not the exact CVE-2023-36727 exploit, but showing the kind of spoofing attackers might use via JavaScript:

<!-- attacker.html -->
<html>
  <body>
    <script>
      // Open a new window pretending to be a trusted site
      var win = window.open("https://trusted-bank.com/login";, "_blank", "width=800,height=600");
      setTimeout(function() {
        // After 2 seconds, replace the page with a phishing site in same window
        win.location = "https://attacker-site.com/fakebank-login.html";;
      }, 200);
    </script>
    <h2>Click here for a surprise</h2>
    <button onclick="window.location.reload()">Surprise</button>
  </body>
</html>

Once the user sees the genuine page, it replaces it with a fake phishing page.

3. Even if the address bar updates, fast-acting users may have already started typing in sensitive information.

For real-world attacks, more advanced obfuscation, timing tricks, or pop-up overlays may be used. Chromium-based browsers, including Edge, have patched several such tricks, but CVE-2023-36727 allowed bypassing these defenses.

4. Exploit Details

A public Proof-of-Concept (PoC) for CVE-2023-36727 was not widely published (likely due to Microsoft’s responsible disclosure programs), but the vulnerability allowed attackers to control how the browser displayed URLs or browser elements.

Scenario:

They click a link opening what appears to be the _real_ Microsoft login page.

- Exploiting CVE-2023-36727, the attacker makes the Edge address bar still show the trusted URL, but the content is controlled by the attacker—collecting user input (phishing).

Potential outcomes:

5. How Was It Fixed?

Microsoft assigned a CVSS score of 6.1 (Medium) and released a fix in Edge version 116..1938.54 and later. The patch blocks the specific JavaScript and window manipulation that enabled spoofing.

- Official Microsoft advisory: CVE-2023-36727 | Chromium-based Microsoft Edge Spoofing Vulnerability
- Patch notes: Edge Release Notes
- Mitre record: CVE-2023-36727 summary
- Reporting acknowledgements: Google Chrome release article
- A look at browser spoofing: OWASP: User Interface Spoofing

7. Conclusion

CVE-2023-36727 highlights how even modern browsers can let attackers manipulate what you see, breaking the fundamental security promise that “the address bar tells the truth.” Always keep browsers up-to-date, double-check URLs, and beware of email links—even Edge and Chrome aren’t immune to fast-moving exploits like this one.

Stay safe and share this info with your friends and colleagues!


If you want to know more about how browser security works or need help checking your browser’s security, let us know in the comments.


Disclaimer: The code is for educational demonstration only. Don’t use it for malicious purposes. Always report security vulnerabilities to the vendors.

Timeline

Published on: 09/15/2023 22:15:13 UTC
Last modified on: 09/20/2023 19:47:58 UTC