CVE-2023-30538 - Discourse Platform Vulnerability due to Improper Sanitization of SVG Files

The Discourse platform is widely known as an open-source software designed for community discussions. Recently, a vulnerability, named CVE-2023-30538, has been identified, which results from the improper sanitization of SVG files. This vulnerability allows attackers to execute arbitrary JavaScript on users' browsers by uploading a carefully crafted SVG file. In this detailed post, we will discuss the exploit details, code snippet, mitigation, and links to original references of the identified vulnerability.

Exploit Details

For a malicious user, exploiting the vulnerability starts with crafting an SVG file containing embedded JavaScript. When the attacker uploads this SVG file on the Discourse platform, the victim’s browser, upon accessing the SVG file, will execute the embedded JavaScript code without proper sanitization. This allows the malicious actor to have control over the victim's browser, which can lead to further security issues.

Let's take a look at an example of a crafted SVG file with embedded JavaScript

<svg xmlns="http://www.w3.org/200/svg">;
  <script>
    alert('This is a CVE-2023-30538 vulnerability test!');
  </script>
</svg>

In the above snippet, a simple alert box will be displayed when the SVG file is accessed. Keep in mind that an attacker can use more sophisticated JavaScript code to cause more significant harm.

Mitigation

To fix this issue, the Discourse team has already patched the vulnerability in the latest stable and tests-passed versions of their platform. It is highly recommended for users to upgrade to these patched versions.

For users who cannot upgrade their platform right away, there are two possible workarounds

1. Enable CDN handling of uploads: It is advisable to use a Content Delivery Network (CDN) to handle user file uploads, which sanitizes SVG files before making them available to users.

2. Disable SVG file uploads: Make sure that the authorized extensions site setting does not include svg. You may also reset the setting to its default configuration, as Discourse does not enable SVG uploads by users by default.

For more information on this vulnerability and its mitigation, you can refer to the following links

1. Discourse's official announcement about the vulnerability: Discourse CVE Announcement
2. Technical details of the vulnerability from the NIST National Vulnerability Database: NVD - CVE-2023-30538

Conclusion

It is of utmost importance to keep security issues and vulnerabilities in mind while using any software, especially an open-source platform like Discourse. Make sure to apply the recommended patches, use reliable CDNs, and configure settings appropriately to stay safe from this vulnerability, CVE-2023-30538.

Timeline

Published on: 04/18/2023 22:15:00 UTC
Last modified on: 04/28/2023 03:50:00 UTC