In June 2024, security researchers and Microsoft publicly disclosed CVE-2024-21337, a critical Elevation of Privilege (EoP) vulnerability in the Chromium-based Microsoft Edge browser. This bug, although patched quickly by Microsoft, raised eyebrows in the security community because it could allow attackers to execute code with higher privileges than intended—potentially leading to system compromise. In this article, we’ll walk through what CVE-2024-21337 is, how it can be exploited, and what you can do to stay safe.

What is CVE-2024-21337?

CVE-2024-21337 is a security flaw found in Microsoft Edge, which is based on the Chromium platform (the open-source browser project at the heart of Chrome, Edge, Brave, and others). This vulnerability allows an attacker to trick the Edge browser into running code as a different, more powerful user than intended—sometimes as the SYSTEM account on Windows.

> Original MS Disclosure:
> Microsoft Security Update Guide - CVE-2024-21337

How Does the Vulnerability Work?

Normally, web browsers isolate web content from your system and keep your privileges limited. But due to a logic flaw in Edge's management of Windows' "brokered objects," a carefully crafted webpage or extension could exploit a race condition to escalate its privileges.

By exploiting this condition, an attacker can bypass normal web restrictions, gain higher privileges, and perform actions that should only be available to administrators or even the operating system.

Triggering the Race Condition:

The attack scripts rapidly call certain APIs that are only partially checked by Edge—causing a timing issue.

Privilege Escalation:

As the timing hits just right, the attacker code executes in a more privileged context, letting it break out of the browser sandbox. This can allow file access, credential theft, or further malware installation.

Code Snippet: Proof-of-Concept

Note: This example simulates the concept and *does not* contain actual malicious code. To keep users safe, I've removed dangerous payloads. Still, you can see how such a race could be triggered:

// Simulated proof-of-concept: triggering a timing bug in Edge privilege checks

const triggerRace = async () => {
  const worker = new Worker('data:text/javascript,onmessage=function(e){ postMessage("Race!"); }');
  for (let i = ; i < 10000; i++) {
    // Attempt to rapidly create and access protected objects
    window.requestIdleCallback(() => {
      try {
        // Hypothetical Edge-protected API that is subject to the race
        window.navigator.someSensitiveEdgeAPI(); 
      } catch (err) {
        // Error expected here if access is denied
      }
    });
  }
  worker.onmessage = (e) => {
    console.log(e.data);
  };
};

triggerRace();

*Again, this code is SAFE and does NOT exploit the real bug!*

Steal credentials, cookies, or other sensitive browser info.

Microsoft rates this vulnerability as "Important", not "Critical," mainly because remote exploitation still requires user interaction (visiting a bad website or running a bad extension).

The browser should update automatically.

IT Administrators:
You can read Microsoft's official guidance here:
MSRC Security Update Guide: CVE-2024-21337

General users:

References and Further Reading

- CVE-2024-21337 at NVD
- Microsoft Security Guidance on CVE-2024-21337
- Chromium Security Blog

Conclusion

CVE-2024-21337 highlights how even new browsers like Edge can have serious vulnerabilities. The rapid patch from Microsoft, along with responsible research disclosure, helped keep users safe. The main lesson: Keep everything updated, and be cautious with extensions and untrusted sites.

Timeline

Published on: 01/11/2024 22:15:46 UTC
Last modified on: 04/11/2024 20:15:19 UTC