In late 2023, the Chrome browser faced a serious security flaw tracked as CVE-2023-5997. This “use-after-free” vulnerability targeted Chrome’s garbage collection system and had some worrying implications—it allowed attackers to remotely exploit heap memory corruption just by tricking users into visiting a specially crafted web page. This post will break down what happened, how an attacker could exploit the bug, and show some real code snippets with references to dig deeper.

What is CVE-2023-5997?

CVE-2023-5997 is a use-after-free bug within the garbage collector (GC) in Google Chrome. Garbage collectors recycle memory in JavaScript engines. If something goes wrong—like accessing memory after it’s freed—attackers can use this to run arbitrary code.

Component: Garbage Collector (V8 Engine)

- Chromium bug: chromium:1496368
- Official advisory: Google Chrome Release Note

Why is Use-After-Free Dangerous?

Use-after-free (UAF) occurs when a program keeps using memory that was already given back to the system. When this happens in web browsers, an attacker can manipulate freed memory through JavaScript, paving the way for _remote code execution_. Because browsers run untrusted code from the web, UAF bugs are particularly severe.

Chrome’s garbage collector handles cleaning up memory used by JavaScript objects. When the logic gets confused—like marking an object as gone but still referencing it elsewhere—attackers step in.

Create objects in Javascript that interact with Chrome’s garbage collector.

2. Force the garbage collector to free a chunk of memory while still keeping a reference to it (usually by exploiting a specific sequence of object creation and deletion).

Allocate something new (like an ArrayBuffer) over the freed memory space.

4. Smuggle data in or out—corrupting other objects, reading sensitive data, or controlling program execution.

Let’s look at a very simplified, pseudocode version of how the exploit works.

Code Snippet: Basic UAF Exploitation Flow

// 1. Allocate a victim object
let victim = { payload: "Sensitive Info" };

// 2. Create a helper object that will free victim via some chrome bug
function triggerGC() {
    // Force Chrome to run garbage collection
    for (let i = ; i < 100000; i++) {
        let temp = [1, 2, 3, 4];
    }
}

// 3. Remove references, making victim eligible for GC
victim = null;

// 4. Trigger garbage collection
triggerGC();

// 5. Allocate a new object (could overlap victim's memory)
let evilArray = new ArrayBuffer(666);

// If successful, evilArray may now occupy memory once used by victim
// The attacker further manipulates contents to read/write data or hijack execution

Of course, real-world exploits are way more complex and often use specific JavaScript features, DOM elements, or race conditions to achieve precise timing.

Real-World Exploit Research & Details

Exploit writers would use fuzzing tools (like AFL or ClusterFuzz) and delve into V8’s source code (V8 on Chromium Gerrit) to spot where the collector gets confused. Chromium’s bug tracker (chromium:1496368) lists security researcher Luyao Liu ([@LuyaoLiuBG)] as one discoverer.

Typical exploit paths could use DOM manipulation, canvas, or custom JS arrays to help overlap objects in memory. In production, these exploits are delivered through harmful HTML pages or tricky ad banners.

Patch and Mitigations

Google patched the vulnerability in Chrome 119..6045.159 and later. They hardened the garbage collector to check for lingering references before freeing objects. If you haven’t already, _upgrade Chrome immediately_. Chromium-based browsers (like Edge, Brave, Opera) also issued fixes.

- Official security page: Chrome Security
- V8 Vulnerabilities: V8 Bug Tracker

Use browser sandboxes and turn on security features.

Developers and security folks can also run tools like AddressSanitizer and browser fuzzers to catch classes of these bugs.

Final Thoughts

CVE-2023-5997 shows how even modern, sophisticated browsers can be tripped up by subtle memory management issues. Remote attackers can take advantage of these low-level bugs just using JavaScript and some crafted HTML. Pushing your Chrome or Chromium-based browser to the latest version is the best defense.

References:
- chromium:1496368 - Security Bug Report
- Official Chrome Release Note
- V8 Engine Source

Timeline

Published on: 11/15/2023 18:15:06 UTC
Last modified on: 12/22/2023 13:15:12 UTC