Pydio Cells through 4.1.2 allows XSS. Pydio Cells implements the download of files using presigned URLs which are generated using the Amazon AWS SDK for JavaScript [1]. The secrets used to sign these URLs are hardcoded and exposed through the JavaScript files of the web application. Therefore, it is possible to generate valid signatures for arbitrary download URLs. By uploading an HTML file and modifying the download URL to serve the file inline instead of as an attachment, any included JavaScript code is executed when the URL is opened in a browser, leading to a cross-site scripting vulnerability.