Google Chrome is considered one of the most secure web browsers in use today, but its massive codebase sometimes leaves room for dangerous security bugs. One such vulnerability—CVE-2022-3075—was discovered in early September 2022: "Insufficient data validation in Mojo in Google Chrome prior to 105..5195.102 allowed a remote attacker who had compromised the renderer process to potentially perform a sandbox escape via a crafted HTML page." In simple terms, this vulnerability let an attacker break out of Chrome’s main security barrier, the sandbox, using a webpage.

In this deep dive, we’ll break down how it worked, show you what the code looked like, include references, and explain why it was so dangerous.

What Is Mojo?

First, it helps to know a little about Mojo. In Chrome, Mojo is an IPC (Inter-Process Communication) library that lets different parts of Chrome (renderer, gpu process, etc.) safely talk to each other. These pieces are separated for security, so a bug in how they communicate (“insufficient data validation”) can allow code to escape the sandbox and affect the rest of your computer.

Breaking Down CVE-2022-3075

Before Chrome 105..5195.102, a bug in Mojo meant that when data was passed between the renderer process (which displays web content) and browser process, it wasn’t always properly checked. If an attacker had already exploited a weaker bug to run code in the renderer, they could use this Mojo bug to send malicious data to other parts of Chrome.

Attack Steps

1. Compromise Renderer Process: The attacker gets arbitrary code execution inside the renderer—usually through another exploit (for example, a JavaScript bug).

Crafted HTML Page Delivers Payload: A special HTML page could send malicious Mojo messages.

3. Insufficient Validation: The browser process accepts the malicious data because it doesn’t strictly check it.
4. Sandbox Escape: The attacker runs code outside the renderer’s sandbox, potentially taking control of the whole browser or even the system.

Example: How an Exploit Might Look

While the actual Chrome code is in C++, the kind of attack comes from *crafted messages* sent from JavaScript running in a web page.

Imagine code like this in attacker’s page

<script>
// Attacker’s payload
async function breakOut() {
  // Abuse a vulnerable interface exposed through Mojo
  // "window.chrome" exposes some internal APIs to JS

  // Example: Send data beyond expected boundaries
  let malicious_data = new Array(1024).fill("A").join('');
  
  // This is a simplification - in reality, attackers locate an exposed Mojo interface and call it
  if (window.someMojoInterface) {
    try {
      window.someMojoInterface.doSomethingEvil(malicious_data);
    } catch (e) {
      console.log("Attack failed or blocked!");
    }
  }
}

breakOut();
</script>

Note: In real cases, attackers might use chrome.webview.postMessage or other available hooks to send malformed data to the browser process. The *core bug* is that the browser process didn't check whether the message was valid or not—it just accepted it.

Vulnerable Code (Hypothetical C++ Snippet)

Here's a simplified version of what a risky Mojo message handler might look like (note: actual Chrome code is much more complex):

void MojoHandler::OnDoSomething(const std::string& input) {
  // Lacking proper input validation!
  // Should check length, content, expected format, etc.
  ProcessInput(input); // This could trigger unsafe behavior if input is malicious!
}

What Makes This So Dangerous?

Chrome’s main defense against browser exploits is its sandbox. Inside the sandbox, exploits are contained and (ideally) can’t get to your files or system resources. CVE-2022-3075 offered attackers a way to *break out* of this sandbox using a bug in how Chrome’s processes talk.

Google issued a quick fix—as shown in their blog post:

> *“Google is aware of reports that an exploit for CVE-2022-3075 exists in the wild.”*

Upgrades to Chrome 105..5195.102 and above close the hole. If you’re still on an older version, update immediately.

References and Further Reading

- Official CVE-2022-3075 entry at NVD
- Google Chrome Stable Channel release notes
- Mojo documentation
- Detailed postmortem from Project Zero (not specific to this bug but explains Chrome sandbox escapes)

Conclusion

CVE-2022-3075 reminds us how critical input validation is, particularly at process boundaries like Mojo. When browser sandboxes are breached, the attacker can take over not just your browser but potentially your whole system. That’s why browser updates matter. Always stay updated!

For pentesters, bug bounty hunters, and browser developers—you can learn from this bug: never trust data across privilege boundaries, and scrutinize every single IPC handler. Even so-called small bugs can become big dangers.

Timeline

Published on: 09/26/2022 16:15:00 UTC
Last modified on: 10/27/2022 19:54:00 UTC