Greenshift <= 12.8.3 - Missing Authorization to Unauthenticated Private Reusable Block Disclosure via 'gspb_el_reusable_load'

The Greenshift – animation and page builder blocks plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 12.8.3. This is due to missing authorization and post status validation in the `gspb_el_reusable_load()` AJAX handler. The handler accepts an arbitrary `post_id` parameter and renders the content of any `wp_block` post without checking `current_user_can('read_post', $post_id)` or verifying the post status. Combined with the nonce being exposed to unauthenticated users on any public page using the `[wp_reusable_render]` shortcode with `ajax="1"`, this makes it possible for unauthenticated attackers to retrieve the rendered HTML content of private, draft, or password-protected reusable blocks.