Ticket #43757: 43757.4.diff

src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php

@@ -173 +173 @@
                 do_action( 'rest_insert_attachment', $attachment, $request, true );
 
                 // Include admin function to get access to wp_generate_attachment_metadata().
+                require_once ABSPATH . 'wp-admin/includes/media.php';
                 require_once ABSPATH . 'wp-admin/includes/image.php';
 
                 wp_update_attachment_metadata( $id, wp_generate_attachment_metadata( $id, $file ) );