Photo Engine (Media Organizer & Lightroom) <= 6.5.6 - Missing Authorization to Unauthenticated Arbitrary Attachment Deletion and Upload via /?wplr-sync-api 'delete' / 'sync' action

The Photo Engine (Media Organizer & Lightroom) plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 6.5.6 This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for unauthenticated attackers to permanently delete arbitrary media attachments via wp_delete_attachment and upload new attachments to the site, actions that require the upload_files or edit_others_posts capabilities. A Subscriber-level user can obtain their own wplr_auth_token directly from the profile.php page source, because the admin screen guard in Meow_WPLR_Sync_Admin::__construct() is commented out, causing wp_localize_script to leak the token into every admin page view; this token can then be used from a cookie-less HTTP session to invoke destructive actions on the /?wplr-sync-api endpoint.