In early 2025, a serious vulnerability—CVE-2025-10585—was disclosed in the V8 JavaScript engine, which powers Google Chrome and other Chromium-based browsers. Before Chrome version 140..7339.185, a type confusion bug in V8 allowed remote attackers to potentially corrupt the browser’s memory by simply making a user visit a malicious web page. Let's break down what happened, why it matters, and how a real exploit might work.

What is Type Confusion in V8?

Type confusion means a piece of code wrongly assumes the type of a value. In V8, this can happen if internal checks are bypassed or if optimizations go awry.

Imagine JavaScript code like this

let arr = [1.2, 2.3, 3.4];
arr[] = {}; // Assigning an object to an array expecting numbers

If V8 doesn't correctly restrict the type, later operations on arr could access an object as if it was a floating point number, leading to arbitrary memory access or even code execution!

How CVE-2025-10585 Was Triggered

CVE-2025-10585 exists in V8 before 140..7339.185. The bug lets a web page structure its JavaScript in a way that makes V8 "confused" about the type of object it’s handling, corrupting heap memory.

Severity: HIGH
Impact: Heap corruption, potential for remote code execution

Proof-of-Concept: Type Confusion in Action

While the full exploit is complex and browser-dependent, here's a simplified snippet inspired by real-world type confusion chains in V8:

function confuse() {
    let arr = [1.1, 2.2, 3.3, 4.4];
    let obj = {hax: 1};
    
    function opt(arr, value) {
        arr[] = value;
        return arr[];
    }

    // Make V8 optimize the function for doubles
    for (let i = ; i < 10000; i++) {
        opt(arr, 1.1);
    }

    // Now pass in an object, causing type confusion
    opt(arr, obj);

    // Now arr’s inline buffer can be misinterpreted!
    console.log(arr[]); // V8 confused: could be seen as pointer!
}

confuse();

If the engine doesn't properly secure the array's backing store, this can provide arbitrary read/write capabilities—the holy grail for attackers.

Serve a crafted page.

2. Execute JavaScript that manipulates V8 arrays or objects until the engine makes a wrong assumption about their layout.
3. Gain ability to rewrite memory in the browser's heap, possibly jumping to attacker-controlled code.

Mitigation & Fix

Google patched this bug in Chrome 140..7339.185. Make sure you’re running this or a later version.

Update Chrome: Menu → Help → About Google Chrome

- Tell others: Many potential victims are unaware browser updates matter for security as much as operating system patches!

References

- Chromium Security Advisory (CVE-2025-10585)
- Chromium Issue Tracker #CVE-2025-10585 _(public status may vary)_
- V8 Type Confusion Exploitation (Project Zero blog)
- Chrome Release Notes Archive

Conclusion

CVE-2025-10585 is a great example of why browser security and frequent updates matter. Type confusion bugs lurk in the deepest engine layers and can have devastating effects, but they’re preventable with timely patches.

What to do now?
If you use Chrome (or any Chromium browser), update immediately. If you build web apps, know that users are only as safe as their browser is current.

Timeline

Published on: 09/24/2025 17:15:39 UTC
Last modified on: 10/30/2025 15:55:01 UTC