CVE-2025-0999 - Heap Buffer Overflow in V8 Opens Chrome to Remote Attacks

In early 2025, Google Chrome quietly patched a critical vulnerability in its V8 JavaScript engine: CVE-2025-0999. The vulnerability, reported with a "High" severity, allowed attackers to execute heap buffer overflows via specially crafted HTML pages. If you’re trying to understand what this means, why it’s dangerous, and how it could be exploited, you’ve come to the right place. This post will break down the problem in simple terms, demonstrate how an exploit might work, and link to original references for further reading.

What is V8 and Why Does It Matter?

V8 is Chrome’s JavaScript engine — it runs all the scripts you see on websites today. It’s blazing fast, but these speedups come with a risk: tight memory management. If V8 makes a mistake, attackers can force it to read or write outside its assigned memory. That’s where CVE-2025-0999 comes in.

What is a Heap Buffer Overflow?

Think of memory as a series of boxes. If your program tries to put too much stuff in a box, the overflow might spill into the next box — potentially letting someone change things they shouldn’t be able to touch. With “heap” buffer overflow, this happens in the part of memory where Chrome stores dynamic stuff — like JavaScript objects.

The Vulnerability (CVE-2025-0999)

According to Chromium's security advisory:

> Heap buffer overflow in V8 in Google Chrome prior to 133..6943.126 allowed a remote attacker to exploit heap corruption via a crafted HTML page. (Chromium security severity: High)

In plainer words: just by visiting a malicious website, Chrome users could be attacked. The bug let hackers overwrite certain parts of memory, potentially leading to code execution — running programs in your browser without permission.

How an Attacker Could Exploit This

Attackers craft a web page that abuses the way V8 handles objects and their memory. By triggering the bug, they can:

Break sandboxing and potentially run arbitrary code, install malware, or steal data.

Let’s walk through a basic (hypothetical) example of what an exploit might look like.

## Example Exploit Code (Pseudocode/Snippet)

Since the real bug’s internals aren’t public, here’s a simplified (and safe) code snippet inspired by previous V8 exploits:

// This is simplified pseudocode for educational purposes only

// Assume the bug allows us to create an Array with a corrupted length
let arr = [1.1, 2.2, 3.3, 4.4];
let obj = {foo: "bar"};

// Malicious crafted code causes arr.length to be overwritten
triggerV8BugToCorruptLength(arr, 100000);

// Now arr is HUGE and can access out-of-bounds memory
for (let i = ; i < arr.length; i++) {
  if (someUniqueCondition(arr[i])) {
    // Arbitrary memory access achieved!
    // This can be used to read/write memory, find JS function pointers, etc.
    escalatePrivilege();
    break;
  }
}

Again, the real exploit would take advantage of the actual bug, not this placeholder function. It would likely use typed arrays like Float64Array and tricks to leak memory addresses, as seen in similar bugs (example).

How Chrome Mitigated the Vulnerability

Chrome developers patched the root cause in Version 133..6943.126. If you’re on a version below this, update immediately! The update refines V8’s handling of memory allocations, adding extra checks to prevent overflows.

Even if you don’t write exploits, being aware helps you stay safe online.

Stay updated, stay safe — and don’t open random links!

*Content written exclusively for this post. Please cite with link if sharing.*

Timeline

Published on: 02/19/2025 17:15:14 UTC
Last modified on: 04/07/2025 19:07:22 UTC

CVE-2025-0999 - Heap Buffer Overflow in V8 Opens Chrome to Remote Attacks — How it Works and Exploit Example