Google Chrome, used by billions worldwide, always remains a hot target for attackers. One critical flaw identified as CVE-2022-0793 affected Chrome’s Cast function before version 99..4844.51. This post will explain how the vulnerability works, go over a simple proof-of-concept, and provide insights on how attackers could abuse it using malicious extensions. Everything is laid out in plain, simple language for anyone curious about web security.

What is "Use After Free"?

A "Use After Free" happens when a program keeps using memory after it’s been freed up. This can let attackers inject bad code, cause crashes, or even take over a computer. In Chrome’s case, this bug was found in the Cast feature (that thing that sends videos to your TV).

User Action Needed: Install a malicious Chrome extension and interact with it

Original references:  
- Chrome Releases Patch - Feb 2022  
- NVD Info: CVE-2022-0793  

How Attackers Exploit CVE-2022-0793

The bug involves Chrome’s Cast feature and what happens if a crafted extension triggers a sequence of events involving media routing. Here’s a typical attack path:

1. Convince User to Install a Malicious Extension: Sometimes via fake websites, phishing, or bundled downloads.
2. Trigger Allocation and Freeing of Memory: The extension interacts with the Cast API, causing Chrome to free a part of memory.
3. Reuse the Freed Memory: The extension then tricks Chrome into using the "no longer valid" memory with the attacker’s data.
4. Outcome: Could crash Chrome, or worse, run arbitrary code (depending on what fills the freed space).

Simple Code Snippet Example (For Educational Purposes Only)

Below is a simplified extension background script _not dangerous on its own, but shows the pattern used in real exploits_:

// background.js

// Assume user clicks the extension, and it abuses Cast function via messaging
chrome.browserAction.onClicked.addListener(() => {
    // Start a Cast session (simplified)
    chrome.cast.requestSession((session) => {

        // Force session to close unexpectedly (frees internal object)
        session.stop(() => {
            // Now, re-use/re-access the session object
            try {
                // This reference now points to freed memory in Chrome's C++
                session.sendMessage('urn:x-cast:com.somechannel', {msg: 'payload'});
            } catch(e) {
                console.log('Potential use-after-free triggered!');
            }
        });

    });
});

1. The above represents a common "use after free" trigger: Free an object (session.stop), then access it (sendMessage) without re-checking if it’s valid.
2. In real attacks, the payload would carefully craft what is sent, with the goal of corrupting heap memory and hijacking code execution.

What Was Fixed?

Google’s fix made sure that whenever Chrome Cast frees a resource, it marks it invalid _everywhere_, so even if an extension tries to use it, Chrome sees it’s not usable.

For organizations:  
Deploy group policies that restrict extension installation.

More References

- Chrome Vulnerability Rewards for February 2022
- Mitre: CVE-2022-0793 Record
- Heap Exploitation Basics (Chrome Dev Guide)

Conclusion

CVE-2022-0793 is a classic example of how bugs in widely used software like Chrome can get weaponized in the real world — especially when crossed with user-installed extensions. Always keep your browser up-to-date, beware of suspicious add-ons, and if you’re a developer, make sure you handle freed memory securely!

If you found this read helpful, share with fellow web users and stay secure online!

Timeline

Published on: 04/05/2022 01:15:00 UTC
Last modified on: 08/15/2022 11:15:00 UTC