Vendor directory security check
From MoodleDocs
Vendor directory security check
The vendor directory should not be present on public sites.
The vendor directory inside the Moodle dirroot contains various third-party libraries and their dependencies, typically installed by the PHP Composer. It may be needed for local development, such as for installing the PHPUnit framework. But it can also contain potentially dangerous code exposing your site to remote attacks.
It is strongly recommended to remove the directory if the site is available via a public URL, or at least prohibit web access to it.
