XML-RPC: Improve error messages for unprivileged users.

Add specific permission checks to avoid ambiguous failure messages.

Props zieladam, peterwilsoncc, xknown, whyisjake.
Built from https://develop.svn.wordpress.org/trunk@49380


git-svn-id: http://core.svn.wordpress.org/trunk@49139 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-xmlrpc-server.php

@@ -3876,6 +3876,21 @@ class wp_xmlrpc_server extends IXR_Server {
 			return new IXR_Error( 403, __( 'Sorry, comments are closed for this item.' ) );
 		}
 
+		if (
+			'publish' === get_post_status( $post_id ) &&
+			! current_user_can( 'edit_post', $post_id ) &&
+			post_password_required( $post_id )
+		) {
+			return new IXR_Error( 403, __( 'Sorry, you are not allowed to comment on this post.' ) );
+		}
+
+		if (
+			'private' === get_post_status( $post_id ) &&
+			! current_user_can( 'read_post', $post_id )
+		) {
+			return new IXR_Error( 403, __( 'Sorry, you are not allowed to comment on this post.' ) );
+		}
+
 		$comment = array(
 			'comment_post_ID' => $post_id,
 			'comment_content' => trim( $content_struct['content'] ),

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6-beta2-49371';
+$wp_version = '5.6-beta2-49380';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.