Gradio is an open-source Python package designed for quick prototyping. Prior to version 6.6.0, the _redirect_to_target() function in Gradio's OAuth flow accepts an unvalidated _target_url query parameter, allowing redirection to arbitrary external URLs. This affects the /logout and /login/callback endpoints on Gradio apps with OAuth enabled (i.e. apps running on Hugging Face Spaces with gr.LoginButton). Starting in version 6.6.0, the _target_url parameter is sanitized to only use the path, query, and fragment, stripping any scheme or host.