Ticket #30210: 30210.2.patch

src/wp-includes/functions.php

@@ -1204 +1204 @@
 function do_feed() {
         global $wp_query;
 
+        if ( ! $wp_query->have_posts() && ! ( $wp_query->tax_query instanceof WP_Tax_Query ) ) {
+                wp_die( __( 'ERROR: This is not a valid feed.' ), '', array( 'response' => 404 ) );
+        }
+
         $feed = get_query_var( 'feed' );
 
         // Remove the pad, if present.