CVE-2022-4181 - “Use After Free” in Forms — How a Chrome Security Bug Put Browsers at Risk

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Intro: What is CVE-2022-4181?

CVE-2022-4181 is a critical security vulnerability found in Google Chrome (and Chromium-based browsers), formally disclosed in late 2022. This bug lives in the “Forms” component of Chrome, letting remote attackers exploit browsers using a crafted HTML page. Its underlying problem is a classic Use After Free bug, which could allow heap corruption—an avenue for attackers to possibly run malicious code on your machine. It affects all Chrome versions prior to 108..5359.71, and was given a High security rating by the Chromium team.

This post breaks down how it works using simple language, includes some code, and offers tips on protecting yourself.

What is a “Use After Free”?

A "use after free" bug happens when a program continues to use memory after it has been freed or deleted. Imagine Chrome handling a web form:

But, Chrome still tries to use it as if it was valid memory.

4. This can result in weird bugs, crashes—or, in some cases, open the door for hackers to manipulate what's in that chunk of memory.

These bugs are dangerous because attackers can carefully craft an input (like an HTML page) to make Chrome use freed memory in ways that let them take control or crash your browser.

How Did CVE-2022-4181 Happen in Chrome?

Chrome’s engine has a component called Forms, responsible for everything from text fields to checkboxes. In this bug, attackers could cause Chrome to free (delete) an object related to a web form, then trick Chrome into using it again.

The details were reported to Chromium by a security researcher who discovered that by manipulating HTML forms through JavaScript (e.g., removing or editing forms dynamically), you could force Chrome into this unsafe "use after free" state.

Suppose a vulnerable function handles a form submission like this (pseudocode)

FormData* form = GetForm(); // Chrome fetches the form object.
ProcessForm(form); // Processes form (user clicks submit)

DeleteForm(form); // Frees the form's memory after submission.

// But there's still a reference to 'form' elsewhere!
form->TriggerEvent(); // Oops! The object is already freed (dangling pointer).

In real attacks, JavaScript would control when the form is modified or removed

<form id="target" onsubmit="exploit()">
  <input name="input1" />
  <button type="submit">Submit</button>
</form>
<script>
function exploit() {
    let target = document.getElementById('target');
    document.body.removeChild(target); // This frees the form object.
    // If Chrome tries to keep using 'target' after this, boom: use-after-free possible!
}
</script>

If an attacker could predict and control what *new* data lands in the same memory spot, they might hijack Chrome’s control flow to execute code.

Typical outcome: browser crash (denial of service).

This was classified as a remote code execution risk, meaning the attack just needed the victim to visit a malicious webpage—no downloads or extra steps.

Reward: $7,000 (Chromium bug bounty).

Read the official Chrome Release Notes (108..5359.71).

Official References & Patches

- Chromium Security Advisory CVE-2022-4181
- Google Security Blog — Chrome Stable Channel Update
- Commit Fix (Chromium source)

The patch ensures that Chrome doesn’t use objects that have already been freed—typically by making references safer, adding checks, or restructuring when memory is reclaimed.

The fix often involves

- Smart pointers/Reference counting: Make sure nothing tries to use memory that’s already freed.
- More careful object deletion: Don’t delete a form object while other parts of the code might still use it.

Developers also add tests so the problem doesn't reappear.

What Should You Do?

Update your browser now
If you haven’t already, update Chrome (or any Chromium-based browser) to at least version 108..5359.71 or newer.

- How to update Chrome

Don’t ignore browser updates!
Many browser bugs can be exploited simply by visiting a website.

Final Thoughts

CVE-2022-4181 is one more example of how complex browser engines are—and why zero-day vulnerabilities can have such a big impact. This “use after free” bug in Chrome’s forms could have let attackers execute code on millions of systems around the world. Chrome’s security team fixed it quickly, but it highlights why you should always keep your browser up to date, and be wary of suspicious websites.

Timeline

Published on: 11/30/2022 00:15:00 UTC
Last modified on: 05/03/2023 12:16:00 UTC