ProjectSend r2029 contains a reflected cross-site scripting vulnerability in thumbnails-regenerate.php that allows remote attackers to inject arbitrary HTML and JavaScript by supplying unsanitized values in the start_date and end_date GET parameters, which are echoed unescaped into HTML attribute values. Attackers can craft a malicious URL that, when followed by an authenticated victim with edit_settings permissions, executes injected scripts in the application origin to steal session cookies or perform unauthorized actions including user management, file management, and application settings changes.