CVE-2025-52902

Summary

The Markdown preview function of File Browser v2.32.0 is vulnerable to Stored Cross-Site-Scripting (XSS). Any JavaScript code that is part of a Markdown file uploaded by a user will be executed by the browser

Impact

A user can upload a malicious Markdown file to the application which can contain arbitrary HTML code. If another user within the same scope clicks on that file, a rendered preview is opened. JavaScript code that has been included will be executed.

Malicious actions that are possible include:

• Obtaining a user's session token
• Elevating the attacker's privileges, if the victim is an administrator (e.g., gaining command execution rights)

Vulnerability Description

Most Markdown parsers accept arbitrary HTML in a document and try rendering it accordingly. For instance, if one creates a file called xss.md with the following content:

# Hallo

<b>foo</b>

<img src="xx" onerror=alert(9)>
<i>bar</i>

Bold and italic text will be rendered. Also, the renderer used in File Browser will try to display the image and execute the code in the onerror event handler.

Proof of Concept

The screenshot shows that the code from the file mentioned above has actually been executed in the victim's browser:

Recommended Countermeasures

The most thorough fix would be to reconfigure the application's Markdown parser to ignore all HTML elements and only render rich text which is part of the Markdown specification. If HTML rendering is considered to be a required feature, an HTML sanitizer like DOMPurify should be used, preferably in conjunction with a Content Security Policy (CSP).

Timeline

• 2025-03-25 Identified the vulnerability in version 2.32.0
• 2025-04-11 Contacted the project
• 2025-04-18 Vulnerability disclosed to the project
• 2025-06-25 Uploaded advisories to the project's GitHub repository
• 2025-06-26 CVE ID assigned by GitHub
• 2025-06-26 Fix released with version 2.33.7

References

• DOMPurify
• Original Advisory

Credits

• Mathias Tausig (SBA Research)

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2025-52902 has a CVSS score of 7.6 (High). The vector is network-reachable, low privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.33.7); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-52902? CVE-2025-52902 is a high-severity cross-site scripting (XSS) vulnerability in github.com/filebrowser/filebrowser/v2 (go), affecting versions < 2.33.7. It is fixed in 2.33.7. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2025-52902? CVE-2025-52902 has a CVSS score of 7.6 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2025-52902?
   • github.com/filebrowser/filebrowser/v2 (go) (versions < 2.33.7)
   • github.com/filebrowser/filebrowser (go) (versions <= 1.11.0)
4. Is there a fix for CVE-2025-52902? Yes. CVE-2025-52902 is fixed in 2.33.7. Upgrade to this version or later.
5. Is CVE-2025-52902 exploitable, and should I be worried? Whether CVE-2025-52902 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-52902 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-52902? Upgrade github.com/filebrowser/filebrowser/v2 to 2.33.7 or later.