CVE-2023-4762 - Type Confusion in V8 – Remote Code Execution in Google Chrome Explained

In mid-2023, Google patched a serious vulnerability in Chrome’s JavaScript engine, V8, tracked as CVE-2023-4762. This flaw, categorized as "Type Confusion," let hackers run any command they wanted on a victim’s computer—just by tricking them into visiting a malicious web page. This post breaks down what happened, how it could be exploited, and what it means for Chrome users and web security.

What Is CVE-2023-4762?

CVE-2023-4762 is a Type Confusion bug in V8, the JavaScript engine that powers Chrome and many other browsers. In plain English, Type Confusion happens when the browser gets tripped up about what kind of data it’s handling. For example, it might expect to work with a number (like 5), but instead, it works with a pointer or an object—a serious problem in low-level languages like C++.

This bug was present in Chrome before version 116..5845.179.

The JavaScript code abuses the vulnerability, confusing V8 about what kind of data it’s using.

4. The attacker is able to run arbitrary code on the victim’s system—this could mean malware, stealing data, or taking over the device.

How Type Confusion Exploits Work (Simple Example)

Attackers often use JavaScript features like Arrays and TypedArrays to mess with V8’s memory, creating unexpected situations that lead to type confusion.

Here’s a simplified pseudo-code snippet that shows the idea (note: this does NOT exploit the bug itself):

let arr = [1.1, 1.2, 1.3];
// The attacker tricks V8 into treating this float array as an object array

arr[] = {}; // Now arr stores an object where V8 expects a number

// Due to internal mismanagement, V8 thinks it's still a float array and treats object as a float
// This confusion can let the attacker read or write arbitrary memory

// If successful, attacker can hijack program flow or inject malicious code

Note: Actual, reliable exploits are MUCH more complicated and change often as Chrome is updated.

Reference Links to Original Sources

- Chromium security advisory (release notes)
- NVD entry for CVE-2023-4762
- Chrome blog summary of Type Confusion V8 Bugs
- Google Project Zero primer on exploiting V8

Details from the Patch and Technical Write-up

The vulnerability was found by security researcher *Clément Lecigne* of Google's Threat Analysis Group. According to the official Chromium bug tracker entry, the bug was reported on 2023-09-11.

Chrome responded rapidly

> "This bug was reported by Clément Lecigne of Google's Threat Analysis Group. Google is aware that an exploit for CVE-2023-4762 exists in the wild."

That means hackers were already using this bug before it was patched.

To exploit this bug, attackers chain several techniques

1. Memory Corruption: Using type confusion to read/write arbitrary memory.
2. Escape JavaScript Sandboxing: Overwrite pointers or structures in memory to break out of JavaScript controls.
3. Execute Shellcode: Spray shellcode ("malicious instructions") in memory and redirect program flow to it.

*A very rough sketch:*

// Step 1: Type confusion leads to out-of-bounds access
let leak = attacker.getMemoryLeak();

// Step 2: Use the leak to find where to write attacker-controlled code

// Step 3: Overwrite function pointers or vtables in memory

// Step 4: Call the hijacked pointer, trigger malicious code

These steps depend on the attacker's ability to guess or manipulate the browser’s memory layout, which changes from version to version—hence why it only works on unpatched versions.

Summary

CVE-2023-4762 is a critical type confusion issue in V8, patched in Chrome 116..5845.179. It allowed attackers to execute any code they wanted if a victim visited a malicious site. These types of bugs show the importance of browser updates and the ongoing arms race between browser vendors and hackers.

Stay safe. Keep everything up to date. Don’t ignore browser update prompts!

*Sources:*
- https://chromereleases.googleblog.com/2023/09/stable-channel-update-for-desktop_14.html
- https://nvd.nist.gov/vuln/detail/CVE-2023-4762
- https://blog.chromium.org/2023/09/chrome-116--5845-179-security-update.html
- https://googleprojectzero.blogspot.com/2023/06/type-confusion-exploitation-in-v8.html

Timeline

Published on: 09/05/2023 22:15:00 UTC
Last modified on: 09/08/2023 23:37:00 UTC