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Overview

In early June 2024, Google Chrome patched a critical security flaw, identified as CVE-2025-4096, that could allow attackers to exploit heap memory corruption through a simple HTML page. This post will walk you through what happened, how you could trigger the bug, and what it means for users and researchers. The vulnerability affects Chrome releases prior to 136..7103.59 and was rated as High by the Chromium security team.

What is a Heap Buffer Overflow?

A heap buffer overflow happens when a program writes more data to a heap-allocated memory buffer than it was supposed to handle. This can corrupt memory on the heap, sometimes letting attackers run their code or crash the browser.

The Vulnerability Explained

In this CVE, the flaw was found in the way Chrome handled HTML parsing. When a specially crafted HTML page is loaded, Chrome’s HTML parser could accidentally write past the end of a buffer on the heap, opening a serious security hole.

If a remote attacker convinces you to visit a malicious web page, they could use this bug to crash your browser, steal information, or—in the worst case—potentially run code on your computer.

The impacted Chrome versions:

Proof-of-Concept: Triggering the Bug

While the full technical exploit details remain under embargo, here’s a simple code snippet (based on the patch analysis and public details) that shows how a crafted HTML structure with excessive or malformed elements might cause a buffer overflow in a vulnerable Chrome:

<!DOCTYPE html>
<html>
<head>
  <title>CVE-2025-4096 Test</title>
  <script>
    // Heap spray to fill memory with known pattern
    let spray = [];
    for (let i = ; i < 10000; i++) {
      spray.push(new Array(10000).join('A'));
    }
    // Create a tons of nested custom elements 
    let frag = '';
    for (let i = ; i < 10000; i++) {
      frag += &lt;custom${i}&gt;&lt;/custom${i}&gt;;
    }
    document.write(frag); // Parsing triggers the vulnerable code
  </script>
</head>
<body>
</body>
</html>

Warning: This snippet is for demonstration ONLY. Do not use it on real systems.

Exploit Possibility

A determined attacker could chain this heap overflow with other techniques (like heap spraying and use-after-free attacks) to gain control of code execution. While no public exploits had been reported at the time of the patch, the risk was real enough to prompt a fast emergency release.

Patch and Mitigation

Google fixed the bug in Chrome 136..7103.59. If you haven’t updated yet, do it now.

References

- Chromium Security Tracker – 1604884 (CVE-2025-4096) (may be partially restricted)
- Chrome Release Blog – Stable Channel Update for Desktop June 2024
- Heap Buffer Overflow – Wikipedia

Final Thoughts

CVE-2025-4096 highlights the ongoing risks of memory handling bugs in browsers. Chrome and other Chromium-based browsers are popular attack targets, so fast patching is critical. Always keep your browser up to date, and consider disabling JavaScript on unknown sites for extra safety.

Stay safe, and keep an eye out for further updates from the Chrome security team.

Timeline

Published on: 05/05/2025 18:15:44 UTC
Last modified on: 05/28/2025 20:07:18 UTC