Sometimes, a small bug can open the door to big risks, especially in software we use every day. CVE-2022-3309 is one such example—a *use-after-free* flaw found in Google Chrome's Assistant on ChromeOS devices, before version 106..5249.62. This vulnerability allowed remote attackers to potentially escape ChromeOS’s protective sandbox with just a bit of user interaction.

In this long read, we'll break down what the vulnerability is, how it works at a technical level, provide relevant code snippets, link out to official references, and walk through how an attacker might exploit this bug in a real-world scenario. If you’re new to use-after-free vulnerabilities or ChromeOS’s internal workings, don’t worry—we’ll keep the language simple and straightforward.

What’s a Use-After-Free?

Before diving into the details, let’s clarify what a *use-after-free* (UAF) is. In programming, resources like memory are allocated and later released (freed) when no longer needed. If the program keeps using that memory after it’s freed, you get a use-after-free bug.

This is risky: attackers can manipulate the freed memory chunk, cause a program to crash, or, as in the case of CVE-2022-3309, sometimes even run code with more permissions than intended.

The Vulnerability: CVE-2022-3309

Summary:  
A use-after-free in the Assistant component in Google Chrome on ChromeOS before version 106..5249.62. A remote attacker who convinces a user to interact with the UI in a specific way could use this bug to break out of the sandbox.

Severity: Medium (Chromium severity rating)

CVE Details:  
- Chromium Issue 1355093  
- NVD Entry - CVE-2022-3309

Where’s the Bug?

The issue was in how Chrome’s Assistant handled user interface objects. The Assistant component would free up UI resources once it believed the user had finished, but certain user gestures could trick it into reusing those freed resources.

The real code is much more complex, but here's a simplified version to show what might go wrong

// Step 1: Create UI component
AssistantView* view = new AssistantView();

// Step 2: User triggers a gesture/click that schedules deletion
view->ScheduleDeletion(); // This will call 'delete view;' soon

// Step 3: Before deletion finishes, another gesture tries to access it
view->ShowResult(); // Oops! The object might already be deleted.

When ShowResult() is called on an object that's already been deleted, unpredictable things can happen. Attackers can try to take advantage of this window of time to exploit the process.

Here’s a hypothetical attack chain

1. Malicious Web Page: An attacker hosts a web page that asks the user to click on a button or perform some gesture.
2. Trigger Complex UI Interaction: Through a combination of scripted events and social engineering (e.g., "Click here quickly twice!"), the attacker manipulates the Assistant’s UI state.

Use-After-Free Triggered: This causes ChromeOS’s Assistant to use already-freed memory.

4. Memory Corruption: The attacker places controlled data in memory, hijacking normal execution flow.
5. Sandbox Escape: If successful, the attacker can execute code *outside* the ChromeOS sandbox, gaining access to things they shouldn’t.

Proof-of-concept (POC):

No public exploit code is known, but theoretical steps would look like this

// This script would run in a malicious web page
// It relies on user interaction to manipulate the Assistant's UI

document.getElementById('trickButton').onclick = function() {
    // Simulate UI interactions that race AssistantView objects:
    openAssistant(); // Show Assistant
    setTimeout(() => {
        closeAssistant(); // Quickly close
        // User clicks rapidly during this process, triggering the UAF
    }, 100);
};

Note: The above JavaScript is illustrative; actual exploitation would require deep knowledge of ChromeOS internals and the ability to reliably trigger the use-after-free.

Fix and Mitigation

Google fixed this issue in ChromeOS 106..5249.62. If you’re on an older version, update NOW.

Always keep ChromeOS updated.

- Be cautious about interacting with web pages that ask you to perform strange gestures or repeated clicks.

References

- Chromium Security Advisory for CVE-2022-3309
- Chromium Issue 1355093 (Restricted details)
- NVD CVE-2022-3309 Listing
- Google Chrome Releases
- What is Use-After-Free? (OWASP)

Conclusion

CVE-2022-3309 is a reminder that even user interface bugs can be critical—especially when clever attackers mix memory management mishaps with browser sandbox protections. The best way to stay safe is to keep ChromeOS up to date, and remember: be cautious when sites ask you to interact in unexpected ways—they might be setting you up for more than you bargained for.

Timeline

Published on: 11/01/2022 20:15:00 UTC
Last modified on: 12/09/2022 15:49:00 UTC