Intro: The Mozilla Firefox web browser recently identified a security vulnerability, CVE-2022-28283, which could impact developers when using the browser's devtools. In this detailed post, we'll discuss the vulnerability, its implications, and how to fix it to ensure safer browsing and development practices.

Vulnerability details

CVE-2022-28283 is a security vulnerability that affects Firefox versions prior to 99. More specifically, the breach lies in the sourceMapURL feature of the browser's devtools. As a result, the lack of proper security checks can potentially allow a webpage to attempt to include local files or other files that should have been inaccessible.

The issue revolves around the inclusion of source maps as a means of debugging in the web browser. Source maps help developers understand how their code is transformed during minification, transpiling, or other similar processes. Firefox devtools use the sourceMapURL feature to locate and process these maps.

Mozilla Reference:

Exploit example

Given the absence of adequate security checks in the sourceMapURL feature, a malicious website could potentially exploit this vulnerability by including a source map URL that points to sensitive files on the user's local filesystem or other inaccessible files.

Here's a code snippet of how the exploit could theoretically occur

<!DOCTYPE html>
  <script src="script.min.js" crossorigin></script>

In this example, "script.min.js" is a minified JavaScript file that includes a sourceMappingURL at the end:

//# sourceMappingURL=file:///C:/Users/user/Desktop/sensitive_data.json

In a vulnerable browser, the above commented source map URL could potentially lead to the inclusion of sensitive data or other unavailable files.

Impact and consequences

The consequences of this vulnerability may range from unauthorized access to sensitive data stored on users' machines to potential cross-site scripting (XSS) attacks. This can have severe implications for user privacy and security, as malicious actors could potentially gain access to private information or manipulate a user's browsing session.

Fix and mitigation

Mozilla has addressed this security issue in Firefox 99, so updating to the latest version will ensure that users are protected from this vulnerability. You can check for updates by opening "Help" in the Firefox menu and then selecting "About Firefox". The browser will automatically check for updates and apply them accordingly.

If for some reason you can't update to the latest version, it's essential to avoid visiting suspicious websites and using Firefox devtools on unknown or untrusted pages. This will help minimize the risk of exposure to this vulnerability.


CVE-2022-28283 is a security vulnerability in the Firefox browser's sourceMapURL feature that could potentially allow unauthorized access to sensitive local files. To protect against this vulnerability, update your browser to Firefox 99 or later, and exercise caution while browsing and working with developer tools on unfamiliar web pages.


Published on: 12/22/2022 20:15:00 UTC
Last modified on: 12/30/2022 20:54:00 UTC