copyparty Reflected XSS via Filter Parameter

Summary

Unauthorized reflected Cross-Site-Scripting when accessing the URL for recent uploads with the filter parameter containing JavaScript code.

Details

When accessing the recent uploads page at /?ru, users can filter the results using an input field at the top. This field appends a filter parameter to the URL, which reflects its value directly into a <script> block without proper escaping.
This vulnerability allows for reflected Cross-Site Scripting (XSS) and can be exploited against both authenticated and unauthenticated users, enabling unwanted actions in the victims browser.

PoC

A URL like this will execute alert(1):

https://127.0.0.1:3923/?ru&filter=</script><script>alert(1)</script>