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In October 2022, researchers uncovered a critical vulnerability affecting Google Chrome’s Layout component: CVE-2022-3654. This use-after-free bug could be triggered by a specially crafted HTML page, allowing a remote attacker to potentially achieve heap corruption – a foundational step towards more serious attacks like remote code execution. This long read will break down what the vulnerability is, how it can be exploited, provide code snippets, and suggest defense strategies. Let’s get started.
What is Use-After-Free?
Use-after-free (UAF) vulnerabilities occur when a program continues to use a pointer after the memory it points to has been freed. In browsers like Chrome, UAF bugs are especially dangerous because attackers can manipulate the heap to place malicious code in freed regions, potentially hijacking control flow.
Bug class: Use-After-Free (UAF)
- Exploitability: Remote/HTML page
Official advisory:
https://chromereleases.googleblog.com/2022/10/stable-channel-update-for-desktop_27.html
Chromium bug:
https://bugs.chromium.org/p/chromium/issues/detail?id=1365136 (may be restricted)
How Was It Discovered?
The bug was discovered by a member of Google’s Project Zero, the in-house security research team, and reported internally. The Chromium Security Team rated it High due to its exploit potential: attackers can send malicious webpages that, when rendered, corrupt Chrome’s memory space.
The Vulnerability – Technical Short Summary
The flaw exists in the handling of certain layout objects during DOM tree manipulation in Google Chrome's Blink rendering engine. When an attacker triggers a specific series of actions (involving elements being added/removed/modified in the DOM), a layout object gets freed (deleted), but a stale pointer to it remains in use, resulting in a UAF.
Core scenario
1. Render/layout object is created for a DOM node.
Through crafted JavaScript, the attacker causes the DOM node to be removed or altered.
3. The layout object is freed but still referenced elsewhere and can be used again, leading to read or write to freed memory.
Here’s a sample HTML+JavaScript snippet that reflects the typical bug-trigger scenario
<!DOCTYPE html>
<html>
<body>
<div id="victim">Hello</div>
<script>
function triggerUAF() {
let victim = document.getElementById('victim');
// Force layout
victim.offsetHeight;
// Remove the victim div, freeing associated layout object
victim.remove();
// Perform actions (like style recalculation or complex DOM modifications)
// forcing further layout processing which uses the now-freed object
document.body.offsetHeight;
}
setTimeout(triggerUAF, 100);
</script>
</body>
</html>
> Note: This only demonstrates the rough sequence; actual exploitation requires deeper heap manipulation and race control.
Real-world Exploit Flow
1. Heap grooming: Populate the heap so that when the freed memory is re-allocated, attacker controls its contents.
2. Trigger UAF: Use DOM and layout operations (as shown above) to free the layout object but leave a dangling pointer.
3. Memory reuse: Immediately reuse the freed memory (by allocating ArrayBuffers, TypedArrays, or large strings).
4. Control EIP/RIP (advanced): Craft the heap-sprayed payload so that, when the stale pointer is used, code execution is achieved – possibly leading to sandbox escape.
Example Exploit Skeleton
Here’s a simplified skeleton on how one might proceed after triggering a UAF (for educational purposes, not weaponized):
function heapSpray() {
let arr = [];
for (let i = ; i < 10000; i++) {
// Fill heap with controlled objects, e.g., ArrayBuffers
arr.push(new ArrayBuffer(x100));
}
}
function trigger() {
// Step 1: Spray the heap
heapSpray();
// Step 2: Attempt UAF trigger
triggerUAF();
// Step 3: Interact with memory to escalate the bug
// This step requires specialized knowledge on ownership and reference structure in Chrome’s Blink engine
}
setTimeout(trigger, 200);
This kind of script typically needs to be enhanced with precise heap manipulation, information leaks, and memory-disclosure techniques.
Why Is This Serious?
Chrome’s layout engine operates at a critical trust boundary between user-supplied content and system resources. UAF bugs here can be chained with other browser vulnerabilities to escape the browser sandbox or execute arbitrary code:
- Remote Code Execution (RCE): Attacker gains total control over the victim’s browser session – deploy spyware, steal credentials, access files.
- Bypasses browser security: UAFs can corrupt security objects or pointers, letting attacks bypass Same-Origin Policy, CORS, memory-safe APIs.
Patch and Mitigation
First and foremost:
Update Chrome – Ensure you are running version 107..5304.62 or later.
Consider additional endpoint protection to detect exploit attempts.
Developers/Researchers:
Review relevant code changes and best practices in pointer ownership and lifecycle management.
Chromium Patch (Reference):
Chromium Gerrit: Commit
*Note: Patch might be merged in a larger commit; the exact UAF fix often involves adding proper smart-pointer use or adjusting reference release timing.*
## Further Reading / References
- Chromium Security Blog: UAF vulnerabilities
- Google Bug Bounty Hall of Fame
- NIST NVD: CVE-2022-3654
- Overview of Use-After-Free in C++
Use strong endpoint monitoring: Many UAF exploits can be caught by behavioral protection tools.
- For devs: use smart pointers: Rust, modern C++, and proper code review dramatically reduce lifetime bugs like UAF.
Tinkering with browser bugs is risky and may be illegal if done outside of research or bug bounty programs.
TL;DR:
CVE-2022-3654 is a critical use-after-free vulnerability in Google Chrome's Layout component that, prior to version 107..5304.62, allowed attackers to exploit heap corruption via malicious webpages. Always keep browsers up-to-date and heed security advisories.
*For more technical details or to contribute to browser security, see the links above and join the Chromium security mailing list!*
Timeline
Published on: 11/01/2022 23:15:00 UTC
Last modified on: 11/25/2022 18:15:00 UTC