CVE-2023-5175: A Deep Dive into the ImageBitmap Crash on Firefox < 118

In recent times, a new vulnerability known as CVE-2023-5175 has been brought to the attention of the cybersecurity community. This vulnerability has been found to affect Firefox versions lower than 118, potentially causing an exploitable crash. This article aims to provide a comprehensive understanding of CVE-2023-5175, including code snippets, exploitation details, and links to original references.

Vulnerability Details

CVE-2023-5175 is actually a use-after-free vulnerability, specifically targeting the ImageBitmap object. In simpler terms, this means that during the shutdown process in Firefox, there is a possibility that an ImageBitmap object is created, which may later be used even after it has been freed—leading to potentially exploitable crashes.

The issue arises specifically from the way web workers handling the postMessage API interacts with the ImageBitmap object. Web workers are a powerful feature allowing developers to run computationally intensive JavaScript code in the background, without affecting the main thread and user interface rendering operations.

Description of the Code Snippet

The following code snippet provides a simplified demonstration of how the vulnerability occurs in affected Firefox versions:

// HTML
<canvas id="canvas"></canvas>

// JavaScript
const canvas = document.getElementById('canvas');
const context = canvas.getContext('2d');

// Create an ImageBitmap from the canvas
createImageBitmap(canvas).then(imageBitmap => {
  const worker = new Worker('worker.js');

  // Transfer the ImageBitmap object to the worker
  worker.postMessage({imageBitmap}, [imageBitmap]);

  // Shut down the worker
  worker.terminate();
});

// worker.js
self.onmessage = ({data}) => {
  const {imageBitmap} = data;
  // Perform operations on the ImageBitmap
  // ...
};

In this example, an ImageBitmap object is created from a <canvas> element on the main page and transferred to a web worker using the postMessage API. The worker then performs computations using the transferred ImageBitmap. However, if the worker is terminated before completing its operations, the ImageBitmap object may still be in use, resulting in a use-after-free scenario.

Exploitation Details

To exploit this vulnerability, an attacker could craft a malicious web page that triggers the vulnerability, causing the user's browser to crash. In the worst-case scenario, a determined attacker could potentially leverage this crash to execute arbitrary code on the user's system, thereby compromising their security and privacy.

To mitigate this vulnerability, Mozilla has released a security update in Firefox 118. It is highly recommended to upgrade to the latest version to ensure that your browser is protected against this attack vector.

Original References

1. Mozilla Foundation Security Advisory 2023-05: https://www.mozilla.org/en-US/security/advisories/mfsa2023-05/
2. Firefox Release Notes: https://www.mozilla.org/en-US/firefox/118./releasenotes/

Conclusion

CVE-2023-5175 is a notable vulnerability that highlights the intricate interactions between web APIs and browser components. This use-after-free issue has the potential to cause exploitable crashes, making it crucial to update Firefox to the latest version. By staying informed and vigilant about the latest security patches, users can ensure that they are taking the necessary steps to protect their digital assets and privacy.

Timeline

Published on: 09/27/2023 15:19:42 UTC
Last modified on: 09/29/2023 13:46:01 UTC