DSGVO Google Web Fonts GDPR <= 1.1 - Unauthenticated Arbitrary File Upload via 'fonturl' Parameter

The DSGVO Google Web Fonts GDPR plugin for WordPress is vulnerable to arbitrary file upload due to missing file type validation in the `DSGVOGWPdownloadGoogleFonts()` function in all versions up to, and including, 1.1. The function is exposed via a `wp_ajax_nopriv_` hook, requiring no authentication. It fetches a user-supplied URL as a CSS file, extracts URLs from its content, and downloads those files to a publicly accessible directory without validating the file type. This makes it possible for unauthenticated attackers to upload arbitrary files including PHP webshells, leading to remote code execution. The exploit requires the site to use one of a handful of specific themes (twentyfifteen, twentyseventeen, twentysixteen, storefront, salient, or shapely).