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What is CVE-2022-21929?

CVE-2022-21929 is a critical remote code execution (RCE) vulnerability that was found in Microsoft Edge (Chromium-based). Unlike its neighbors CVE-2022-21930 and CVE-2022-21931, this vulnerability specifically enables an attacker to run malicious code on your computer simply by getting you to visit a specially-crafted website.

Why should you care? If you use Edge for browsing, attackers could remotely take control of your device, steal sensitive data, or install malware without your consent. This article breaks down how this CVE works — in plain language — with a technical look under the hood, sample code, and practical references.

Vulnerability Overview

Microsoft Edge switched to Chromium for better compatibility and speed. Like other web browsers, complex memory management makes it risky. CVE-2022-21929 is a "use-after-free" vulnerability, which happens when a program continues to use memory after it’s supposedly freed. If exploited, hackers can get the browser to execute arbitrary code.

Fixed in: Microsoft Edge Stable Channel Release (Google Chrome update integrated)

> Official Microsoft advisory:  
> Microsoft Security Guidance: CVE-2022-21929

How Does CVE-2022-21929 Work?

This bug lives in how Edge handles certain JavaScript objects and processes DOM events. A smart attacker can:

1. Trigger the browser to free a JavaScript object (say, by deleting an element with active event listeners).

Trick Edge into using this freed memory, now possibly under the attacker’s control.

If the freed object gets filled up with the attacker’s code (heap spray), Edge can execute the code when it “reuses” the memory.

Let’s look at a simplified version of how such a use-after-free can be tried in a browser

// Example: forcing Edge to access a deleted object
let victim = document.createElement('div');

victim.addEventListener('click', function handler() {
    // Remove the element and free memory
    victim.parentNode && victim.parentNode.removeChild(victim);
    victim = null;
    // Heap spray attempt
    for (let i = ; i < 10000; i++) {
        let sprayer = new Array(100).fill("A".repeat(100));
        window["spray" + i] = sprayer;
    }
    // ...potentially force browser to use-after-free the original 'victim'
});

document.body.appendChild(victim);
victim.click();  // Simulate user action to trigger vulnerability

Note:
This code is a simple illustration and NOT a working exploit. Crafting a fully working exploit is complex and involves advanced heap manipulation, which is tailored to the exact browser engine's inner workings and version.

What Happens If Exploited?

If the exploit is successful, the browser may execute attacker-supplied code with the same privileges as the user — which could mean complete compromise of your data and possibly your device.

Update Edge Immediately:

Microsoft patched this bug quickly. Make sure you have the latest version (go to ... > Help and feedback > About Microsoft Edge to auto-update).

Detection

On enterprise networks, unusual Edge processes making outbound connections, or browser crashes with references to heap corruption, may be a sign of exploitation. Microsoft Defender and third-party antivirus software can detect in-the-wild payload attempts.

Microsoft Official Advisory:

- CVE-2022-21929 Details

Edge for Business Security Blog:

- Microsoft Edge Security Updates

Google Project Zero on Use-After-Free Bugs:

- Project Zero: Heap Exploitation

Chromium Security (How the engine is patched):

- Chromium Security Advisories

Conclusion

CVE-2022-21929 is a sharp reminder that even modern browsers have critical security holes. Thankfully, Microsoft has patched this issue and updating your browser is the best and simplest defense.

Stay updated, stay alert — and keep surfing safe!


Have questions, or want more in-depth code samples for browser vulnerability research? Comment below or check the official links above!

Timeline

Published on: 01/11/2022 21:15:00 UTC
Last modified on: 01/20/2022 19:23:00 UTC