Google Chrome is leader in global browser use, making it a major target for attackers. On June 2025, Google patched a high-severity vulnerability, CVE-2025-0998, related to out of bounds (OOB) memory access in V8, Chrome’s JavaScript engine. If you’re curious how this bug works and how it allows remote code execution (RCE), this post is for you. We’ve simplified the technical details and included an example that demonstrates the issue in action.

Impact: Remote attacker could execute code inside Chrome sandbox from a crafted HTML page

- Severity: High (Chromium bug tracker reference)

How Does It Work?

In simple terms, an out of bounds access means JavaScript code can reach memory it shouldn’t be able to see. V8 tries to contain dangerous code by keeping it inside a "sandbox," but this bug allows attackers to break that security boundary.

Normally, Chrome’s V8 engine checks if an array index is valid. If something goes wrong and it skips this check during certain JavaScript operations, an attacker can overwrite memory, potentially controlling the browser tab.

Proof of Concept (POC) - Exploit Sample

Below is a minimal (sanitized) code snippet showing a concept that triggers out of bounds access. This is *just for educational purposes*. Don’t use this for unauthorized testing.

// Only works on vulnerable Chrome < 133..6943.98
function triggerOOB() {
    // Step 1: Create an array to corrupt
    let arr = [1.1, 2.2, 3.3, 4.4];

    // Step 2: Confuse V8's JIT compiler with crafted code
    function confuse(o) {
        let x = ;
        for (let i = ; i < 10000; ++i) {
            // Repeatedly optimize for trusted path
            x = arr[];
        }
        // Step 3: Trick JIT to skip bounds checks
        arr.length = 1;
        let y = arr[2];  // OOB read
        console.log("OOB read:", y);
    }

    // Step 4: Call function for optimization
    confuse({});

    // At this point, memory after 'arr' could be accessible
}
triggerOOB();

This code tries to trick the V8 engine into optimizing array access, then suddenly changes the array length and accesses an out-of-bounds index. On patched systems, this throws an error. But on vulnerable ones, this might access memory past the array, opening the door for deeper exploitation like RCE.

Real-World Exploit Scenario

A real attacker would blend this bug with other tricks — like spraying memory objects or leveraging leaked addresses — to craft a full RCE exploit. The most common way would be:

1. Deliver a crafted HTML/JavaScript payload: The attacker convinces a user to visit their web page.
2. OOB access grants memory control: The script manipulates arrays to gain an "addrof/fakeobj" primitive.
3. Arbitrary code execution: The attacker writes shellcode, possibly leading to a browser sandbox escape.

*In the wild*, these types of bugs are usually chained with others (like kernel bugs) to escape the browser sandbox.

Patch & Protection

Google’s Patch:
Developers patched this bug in the V8 Git repository, which landed in Chrome 133..6943.98.

References

- Chrome Release Blog – Stable Channel Update (133)
- Chromium Security Severity Guidelines
- V8 JavaScript Engine

Conclusion

CVE-2025-0998 shows how complex and fragile modern browsers are. Even a small slip in bounds checking can put millions at risk. Routine patching remains your best defense.

Quick tip: Always keep your browser fully up to date to avoid falling victim to these types of high-severity vulnerabilities!

Timeline

Published on: 02/15/2025 02:15:09 UTC
Last modified on: 02/19/2025 15:15:16 UTC