Index: wp-admin/includes/media.php
===================================================================
--- wp-admin/includes/media.php	(revision 23314)
+++ wp-admin/includes/media.php	(working copy)
@@ -2349,7 +2349,7 @@
 function attachment_submitbox_metadata() {
 	$post = get_post();
 
-	$filename = esc_html( basename( $post->guid ) );
+	$filename = esc_html( wp_basename( $post->guid ) );
 
 	$media_dims = '';
 	$meta = wp_get_attachment_metadata( $post->ID );
Index: wp-includes/media.php
===================================================================
--- wp-includes/media.php	(revision 23314)
+++ wp-includes/media.php	(working copy)
@@ -1326,7 +1326,7 @@
 	$response = array(
 		'id'          => $attachment->ID,
 		'title'       => $attachment->post_title,
-		'filename'    => basename( $attachment->guid ),
+		'filename'    => wp_basename( $attachment->guid ),
 		'url'         => $attachment_url,
 		'link'        => get_attachment_link( $attachment->ID ),
 		'alt'         => get_post_meta( $attachment->ID, '_wp_attachment_image_alt', true ),