CVE-2025-52902 is a high-severity (CVSS 7.6) Cross-site Scripting (XSS) vulnerability in github.com/filebrowser/filebrowser/v2. A fix is available for github.com/filebrowser/filebrowser/v2 — see the affected versions and patch details below.
File Browser has Stored Cross-Site Scripting vulnerability
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-52902.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
github.com/filebrowser/filebrowser/v2🐹github.com/filebrowser/filebrowserReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
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
2025-03-25Identified the vulnerability in version 2.32.02025-04-11Contacted the project2025-04-18Vulnerability disclosed to the project2025-06-25Uploaded advisories to the project's GitHub repository2025-06-26CVE ID assigned by GitHub2025-06-26Fix released with version 2.33.7
References
Credits
- Mathias Tausig (SBA Research)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/filebrowser/filebrowser/v2 | all versions | 2.33.7go get github.com/filebrowser/filebrowser/v2@v2.33.7 |
| 🐹Go | github.com/filebrowser/filebrowser | all versions | No fix |
Affected Products
filebrowserfilebrowserDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/filebrowser/filebrowser/v2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/filebrowser/filebrowser/v2 to 2.33.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-52902 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2025-52902 in your dependencies?
Find it across Go, including transitive dependencies.