Ticket #51773: patch.diff

src/wp-includes/functions.php

@@ -5513 +5513 @@
                                 $directory = str_replace( ABSPATH, '', $script_filename_dir );
                                 // Strip off the subdirectory, and any file/query params.
                                 $path = preg_replace( '#/' . preg_quote( $directory, '#' ) . '/[^/]*$#i', '', $_SERVER['REQUEST_URI'] );
-                        } elseif ( false !== strpos( $abspath_fix, $script_filename_dir ) ) {
+                        } elseif ( '' !== $script_filename_dir && false !== strpos( $abspath_fix, $script_filename_dir ) ) {
                                 // Request is hitting a file above ABSPATH.
                                 $subdirectory = substr( $abspath_fix, strpos( $abspath_fix, $script_filename_dir ) + strlen( $script_filename_dir ) );
                                 // Strip off any file/query params from the path, appending the subdirectory to the installation.