JupyterLab: Argument injection in JupyterLab extension uninstall exposes server-readable files and internal URLs

JupyterLab's PyPI extension manager runs python -m pip uninstall with the extension name taken from the request body. ExtensionHandler.post validates the name for cmd=install but not for cmd=uninstall, so a name that begins with - reaches the command line and pip reads it as an option rather than...