Gutenberg Blocks with AI by Kadence WP <= 3.6.1 - Authenticated (Contributor+) Server-Side Request Forgery via 'endpoint' Parameter

The Gutenberg Blocks with AI by Kadence WP plugin for WordPress is vulnerable to Server-Side Request Forgery in all versions up to, and including, 3.6.1. This is due to insufficient validation of the `endpoint` parameter in the `get_items()` function of the GetResponse REST API handler. The endpoint's permission check only requires `edit_posts` capability (Contributor role) rather than `manage_options` (Administrator). This makes it possible for authenticated attackers, with Contributor-level access and above, to make server-side requests to arbitrary endpoints on the configured GetResponse API server, retrieving sensitive data such as contacts, campaigns, and mailing lists using the site's stored API credentials. The stored API key is also leaked in the request headers.