June 2023 exploded with news of yet another high-severity Chrome security flaw. CVE-2023-3215, a use-after-free bug in the WebRTC component, put billions of users at risk – and all it took was a malicious HTML page. In this deep dive, we'll break down how the bug works, show a simplified proof of concept, and explain how attackers could have leveraged it to corrupt memory and potentially run any code they liked.

What is WebRTC, and Why Does it Matter?

WebRTC (Web Real-Time Communication) is the engine inside Chrome (and many other browsers) that powers video calls, voice chat, and peer-to-peer file sharing right in your browser — no downloads needed. Built for speed, it’s complex and processes huge amounts of user data. It's a juicy target for hackers.

Understanding the Vulnerability

CVE-2023-3215: Use after free in WebRTC in Google Chrome prior to 114..5735.133 allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page. (Chromium security severity: High)

> In plain English: Chrome accidentally kept using a chunk of memory for WebRTC _after_ it had already been deleted (freed). If an attacker could trick you into visiting a bad website, they could take control of that memory and corrupt or even run arbitrary code on your computer or phone.

Root Cause

- When WebRTC handles real-time data, it sometimes _frees_ (deletes) parts of memory that are still in use, especially if several JavaScript events fire in an unusual order.
- After freeing it, code still _uses_ that same piece of memory (now "dangling"), which is dangerous since anyone could fill it with something else.

Google themselves described the risk here

- Chromium Issue 1459987 (open after fix): "Use after free in WebRTC. Reported by wg1@a11y.com on 2023-06-08"

1. User visits a crafted HTML page

This page uses JavaScript to rapidly open and close WebRTC connections, triggering the bug.

2. Memory gets freed, but still in use

The old memory is "freed" but some Chrome code still tries to use it.

3. Heap corruption

If the attacker can "spray" the heap (allocate lots of predictable data), they might control what lands in that spot – then steer Chrome's execution flow.

4. Possible arbitrary code execution

Once an attacker gets code running in the browser’s process, all bets are off: they could install spyware, steal passwords, or pivot deeper.

Simplified Proof-of-Concept (PoC)

Here’s a SIMPLIFIED snippet showing the category of actions an attack page might take. (Not a full working exploit, for safety)

<!-- Example: Stress the WebRTC layer to trigger the UAF -->
<html>
<head>
  <title>CVE-2023-3215 PoC (Simulated)</title>
</head>
<body>
  <script>
    const peers = [];
    function sprayAndFree() {
      // Create 100 peer connections
      for (let i=; i<100; i++) {
        let pc = new RTCPeerConnection();
        peers.push(pc);

        // Intentionally do weird things with transceivers
        pc.addTransceiver('audio');
        // Rapidly close connections to try triggering race condition
        setTimeout(()=>{ pc.close(); }, 10);
      }
    }
    // Spray the memory
    for (let i=; i<200; i++) {
      sprayAndFree();
    }
    // If the bug exists, some freed objects could be used -- causing crash or worse
  </script>
  <h2>WebRTC UAF Stress Test</h2>
</body>
</html>

*Note: This code just triggers lots of creation/destruction. Real attackers use complex heap manipulation and precise timing.*

June 8, 2023: Vulnerability reported privately to Chromium team

- June 13, 2023: Fixed in Chrome 114..5735.133

How Did Google Fix It?

The fix involved making sure WebRTC doesn’t free memory objects until they’re *really* no longer needed. Patch reference here.

- Google Chrome Release Note (June 13, 2023)
- Chromium Bug 1459987
- NIST NVD Entry for CVE-2023-3215
- WebRTC Official Documentation

Final Words

If you run Chrome, check for updates now! CVE-2023-3215 shows how a complex browser feature can open the door for hackers, even with something as routine as video or voice chat. Chrome’s security team was fast and transparent – but it’s a race between attackers and defenders every day.

Stay safe and keep your software updated!

*If you found this breakdown useful, consider sharing it with friends and colleagues. Knowledge is protection!*

Timeline

Published on: 06/13/2023 18:15:00 UTC
Last modified on: 06/27/2023 02:15:00 UTC