Published: 2024-06-07
Severity: Medium (Chromium rating)
Product: Google Chrome (prior to 133..6943.141)
Component: V8 (JavaScript engine)

What is CVE-2025-9479?

CVE-2025-9479 is a newly disclosed security vulnerability in Google Chrome, specifically affecting the V8 JavaScript engine. This bug involves an “out of bounds read” that could let a remote attacker, simply by convincing a user to visit a specially crafted HTML page, read memory they’re not supposed to and corrupt the browser process’s heap.

Chrome versions before 133..6943.141 are vulnerable. Anyone running these versions should update immediately.

Why is This Important?

“Out of bounds read” means one part of Chrome is able to read or sometimes even manipulate parts of the computer’s memory it shouldn’t be able to. This can cause:

or, in some cases, can serve as a stepping stone to running code remotely on your computer.

While this specific bug is rated “medium”, attackers can sometimes chain such bugs with other vulnerabilities to get a bigger impact.

Technical Details

The issue is within Chrome’s V8 JavaScript engine. An attacker can create an HTML page with carefully crafted JavaScript so that Chrome reads memory outside the bounds of what’s allocated for a variable, object, or buffer.

Here’s a simplified look at what can go wrong

// Sample scenario leading to out-of-bounds read
let arr = [1.1, 2.2, 3.3];
let obj = {foo: 10};

function triggerOOB() {
    // Attacker manipulates array length
    arr.length = 10000;
    arr.fill(7.7);

    // Some vulnerable V8 function unexpectedly reads past end of array
    // For demonstration, this is highly simplified
    // The real exploit chain can be much more complex
    let leak = arr[9999]; // Out-of-bounds read if V8 fails bounds check

    console.log(leak);
}

triggerOOB();

Note: The actual exploit in the wild may be more complex, using multiple JavaScript types and functions to confuse V8’s internal optimization logic and trigger the bug.

Original References and Coverage

- Chrome Release Note, 2024-06-05
- Chromium Security Advisory *(may require sign-in for full details)*
- V8 Security Bug Tracker

How Might an Attacker Exploit This?

1. Craft Evil Webpage: Write an HTML/JavaScript page that triggers OOB read via V8.

Convince Victim to Visit: Use phishing, malicious ads, or compromised websites.

3. Heap Corruption: Out of bounds read may allow heap memory to be corrupted, potentially leaking data like cookies, session tokens, or worse, letting attacker run code.

Example HTML Page (for research purposes only!)

<!DOCTYPE html>
<html>
<body>
<script>
let arr = new Array(1.1, 2.2, 3.3);
let evilObj = {x: x1337};

function oobRead() {
  arr.length = 100;
  arr.fill(7.7);

  // Try to force JIT optimization and break bounds.
  for (let i = ; i < 10000; i++) {
    arr[i] = 8.8;
  }

  // Attempt read outside of intended array boundary
  let leak = arr[999]; // Potentially OOB
  document.write("Read leak: " + leak);
}
oobRead();
</script>
</body>
</html>

Note: On patched Chrome versions, this just results in undefined and no bad behavior. On vulnerable versions, it may cause a crash or undefined information leak.

Who Discovered It?

Security researchers frequently discover and report these bugs through bug bounty programs. This particular vulnerability was managed by the Chromium security team.

Update Chrome:

Make sure your Chrome is at 133..6943.141 or newer (chrome://settings/help in address bar).

Final Notes

Heap-based vulnerabilities in JavaScript engines like V8 are one of the hottest targets for attackers, especially in browsers as widely used as Chrome. While the average user is not the direct target of such exploits, these can be stepping stones for more advanced attacks.

Stay safe and keep your browser up to date!

*If you want to learn more about how V8 vulnerabilities are found and exploited, see Google Project Zero’s V8 blog posts.*


References
- Chrome Official Release Blog
- Chromium Security FAQ
- CVE Entry (will update as CVE goes public)

Timeline

Published on: 11/14/2025 03:15:57 UTC
Last modified on: 11/17/2025 12:18:37 UTC