Typemill is a flat-file, Markdown-based content management system designed for informational documentation websites. Versions prior to 2.23.0 are vulnerable to stored HTML attribute injection in the page metadata fields (og:title and og:description). An authenticated user with permission to modify page metadata can inject arbitrary HTML attributes into generated <meta> tags due to missing output encoding. Under certain browser or DOM interaction scenarios, this may lead to stored cross-site scripting (XSS). Version 2.23.0 fixes the issue.