Mercury: Stored / DOM Cross-Site Scripting (XSS): mr.Markdown renders untrusted content as raw, unsanitized HTML

Summary Mercury turns Jupyter notebooks into shared web apps/dashboards. The mr.Markdown widget converts its input to HTML with python-markdown and no sanitization step. MarkdownWidget is an ipywidgets.HTML widget, whose value is written to the page as raw HTML via innerHTML with no sanitization,...