Ticket #25817: 25817.2.patch

src/wp-admin/includes/class-wp-upgrader.php

@@ -1332 +1332 @@
                 if ( !isset( $current->response ) || $current->response == 'latest' )
                         return new WP_Error('up_to_date', $this->strings['up_to_date']);
 
-                $res = $this->fs_connect( array(ABSPATH, WP_CONTENT_DIR) );
-                if ( is_wp_error($res) )
+                $res = $this->fs_connect( array( ABSPATH, WP_CONTENT_DIR ) );
+                if ( is_wp_error( $res ) )
                         return $res;
+                elseif ( ! $res )
+                        return new WP_Error( 'fs_unavailable', $this->strings['fs_unavailable'] );
 
                 $wp_dir = trailingslashit($wp_filesystem->abspath());