CVE-2025-0291 - How Type Confusion in Chrome's V8 Engine Lets Attackers Run Code in Your Browser

It’s 2025, and Chrome is still the world’s most popular web browser, but it’s not invulnerable. A recent vulnerability, CVE-2025-0291, caught the eyes of security professionals — and criminals — everywhere. This bug affects Chrome versions prior to 131..6778.264 and involves a “type confusion” in the V8 JavaScript engine. Successful exploitation could let a bad actor run arbitrary code inside Chrome's sandbox just by getting you to visit a malicious HTML page.

In this exclusive post, I’ll break down what that means, how it works, and provide a demonstration with code snippets. If you’re a developer, IT admin, or just a curious Chrome user, read on.

What Is Type Confusion?

Type confusion bugs happen when a program assumes a piece of data is one type, but it’s actually another. In languages without strict type checking (like JavaScript, handled by Chrome’s V8 engine), this can be a real headache.

Imagine you have an object that’s supposed to be a String, and the JavaScript engine mistakenly treats it as an Array. If the memory layouts are different, this could lead to writing or reading data in unexpected ways – and that’s often the first step to gaining control over the browser.

How Does CVE-2025-0291 Work?

The problem specifically impacts V8, Chrome’s JavaScript and WebAssembly engine. An attacker can craft JavaScript code in a webpage that tricks V8 into misidentifying the type of a JavaScript object. This gives the attacker the power to manipulate memory locations they shouldn’t control.

Write data to memory locations, possibly corrupting critical browser structures.

- Eventually, execute their own code in Chrome’s sandbox, which can then be used to attack or steal from you.

Severity: HIGH (see Chromium Security Ratings)

Technical Example

Let’s look at what this might look like in code.

Suppose a simplified flow in V8’s JIT (Just-In-Time) compiler forgets to properly check types

function confuse(arr, value) {
    arr[] = value;
    return arr[];
}

let objArray = [ {}, {}, {} ]; // Supposed to only hold objects
let floatArray = [1.1, 2.2, 3.3]; // Supposed to only hold floats

// The exploit triggers optimization, then type confusion
for (let i = ; i < 10000; i++) {
    confuse(objArray, {});
}

// Now, pass a float array but write an object to it!
console.log(confuse(floatArray, {})); // Type confusion!

In older, buggy versions of V8, after the confuse() function gets optimized, it may *no longer check* the type of arr strictly and thus allows storing an object in what is expected to be a float array. This can be leveraged as a first step toward manipulating memory.

An attacker would combine this with more advanced JavaScript techniques—using, for example, ArrayBuffers to read and write arbitrary memory.

Proof of Concept (PoC) Exploit

Here’s a minimal, simplified version to show how exploitation might begin. (For educational purposes only!)

function addrof(obj) {
  let arr = [1.1, 1.2, 1.3];
  arr[] = obj;
  return arr[];
}

let fakeObj = {hacked: true};
console.log(addrof(fakeObj));

Of course, real-world attackers chain several techniques: These initial steps let them get the *address* of an object in memory, and from there, with further tricks, they can achieve arbitrary read/write, and finally code execution.

*NOTE:* This code does not cause exploit on current Chrome, but illustrates the kind of logic an attacker writes.

Links to Details and References

- Chromium Issue 1517815: V8 Type Confusion leading to Code Execution
- Chrome Releases: Security Fixes and Updates
- V8 GitHub Repo
- Relevant Chromium Severity Guidelines

How Was It Fixed?

The V8 team quickly patched the code to add better type checks before memory operations. You can see the public changelog here:
Chromium Change Log for 131..6778.264

Enable Automatic Updates: Chrome does this by default.

- Be Careful What You Click: Attackers might try to lure you to malicious sites using spam, phishing, or malvertising.

Conclusion

CVE-2025-0291 shows how even mature engines like V8 in Chrome can have critical bugs. Type confusion isn’t a new attack, but when it turns into arbitrary code execution via a simple webpage, it’s no small thing. Chrome’s quick update response keeps users safe, but only if you update.

For technical folks: always be wary of assumptions about types and memory. For everyone else: keep your browser up to date, and browse wisely.

Stay safe, and happy (secure) browsing!

*This report is exclusive to our readers. All code snippets are educational. For further reading, see the reference links above.*

Timeline

Published on: 01/08/2025 19:15:38 UTC
Last modified on: 01/08/2025 20:15:29 UTC