FacturaScripts vulnerable to Reflected Cross-Site Scripting (XSS) via Cookie Manipulation

Summary

A Reflected Cross-Site Scripting (XSS) vulnerability exists in the fsNick cookie parameter. The application reflects the cookie's value directly into the HTML without sanitization.

Details

The fsNick cookie is rendered into the DOM without encoding. While the server does reject the modified session and forces a logout, the HTML containing the payload reaches the browser first. This lets the script execute immediately upon load, effectively beating the redirect.

PoC

1. Log in to the application with any valid account. <img width="2078" height="302" alt="image" src="https://github.com/user-attachments/assets/d8a9a779-44e0-4a3e-839f-0a031868fbd5" />

2. Capture any the GET request . <img width="1267" height="276" alt="image" src="https://github.com/user-attachments/assets/22e43f73-4f86-4cab-a074-7aba584a71ac" />

3. Modify the value of "fsNick" with the following JavaScript: <script>alert(window.origin)</script>

4. Send the modified request. <img width="1569" height="319" alt="image" src="https://github.com/user-attachments/assets/ade88db1-aadc-4c50-9e02-d09888067e98" />

5. Result <img width="1217" height="771" alt="image" src="https://github.com/user-attachments/assets/5858fe9f-127a-4845-b484-5a7ef4ae2cb4" />

Impact

The payload executes before the session ends, which could potentially allow for a single unauthorized action before the logout.