diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index df5d209e48..1827dd76fc 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -1699,17 +1699,30 @@ function path_join( $base, $path ) {
  * @since 3.9.0
  * @since 4.4.0 Ensures upper-case drive letters on Windows systems.
  * @since 4.5.0 Allows for Windows network shares.
+ * @since 4.9.7 Allows for PHP file wrappers.
  *
  * @param string $path Path to normalize.
  * @return string Normalized path.
  */
 function wp_normalize_path( $path ) {
+	$wrapper = '';
+	if ( wp_is_stream( $path ) ) {
+		list( $wrapper, $path ) = explode( '://', $path, 2 );
+		$wrapper .= '://';
+	}
+
+	// Standardise all paths to use /
 	$path = str_replace( '\\', '/', $path );
+
+	// Replace multiple slashes down to a singular, allowing for network shares having two slashes.
 	$path = preg_replace( '|(?<=.)/+|', '/', $path );
+
+	// Windows paths should uppercase the drive letter
 	if ( ':' === substr( $path, 1, 1 ) ) {
 		$path = ucfirst( $path );
 	}
-	return $path;
+
+	return $wrapper . $path;
 }
 
 /**
@@ -5445,6 +5458,28 @@ function wp_delete_file( $file ) {
 	}
 }
 
+/**
+ * Deletes a file if its path is within the given directory.
+ *
+ * @since 4.9.7
+ *
+ * @param string $file      Absolute path to the file to delete.
+ * @param string $directory Absolute path to a directory.
+ * @return bool True on success, false on failure.
+ */
+function wp_delete_file_from_directory( $file, $directory ) {
+	$real_file = realpath( wp_normalize_path( $file ) );
+	$real_directory = realpath( wp_normalize_path( $directory ) );
+
+	if ( false === $real_file || false === $real_directory || strpos( wp_normalize_path( $real_file ), trailingslashit( wp_normalize_path( $real_directory ) ) ) !== 0 ) {
+		return false;
+	}
+
+	wp_delete_file( $file );
+
+	return true;
+}
+
 /**
  * Outputs a small JS snippet on preview tabs/windows to remove `window.name` on unload.
  *
diff --git a/wp-includes/post.php b/wp-includes/post.php
index 0d020c11b4..8dc888cc02 100644
--- a/wp-includes/post.php
+++ b/wp-includes/post.php
@@ -4914,42 +4914,79 @@ function wp_delete_attachment( $post_id, $force_delete = false ) {
 	/** This action is documented in wp-includes/post.php */
 	do_action( 'deleted_post', $post_id );
 
-	$uploadpath = wp_get_upload_dir();
+	wp_delete_attachment_files( $post_id, $meta, $backup_sizes, $file );
 
-	if ( ! empty($meta['thumb']) ) {
+	clean_post_cache( $post );
+
+	return $post;
+}
+
+/**
+ * Deletes all files that belong to the given attachment.
+ *
+ * @since 4.9.7
+ *
+ * @param int    $post_id      Attachment ID.
+ * @param array  $meta         The attachment's meta data.
+ * @param array  $backup_sizes The meta data for the attachment's backup images.
+ * @param string $file         Absolute path to the attachment's file.
+ * @return bool True on success, false on failure.
+ */
+function wp_delete_attachment_files( $post_id, $meta, $backup_sizes, $file ) {
+	global $wpdb;
+
+	$uploadpath = wp_get_upload_dir();
+	$deleted    = true;
+
+	if ( ! empty( $meta['thumb'] ) ) {
 		// Don't delete the thumb if another attachment uses it.
-		if (! $wpdb->get_row( $wpdb->prepare( "SELECT meta_id FROM $wpdb->postmeta WHERE meta_key = '_wp_attachment_metadata' AND meta_value LIKE %s AND post_id <> %d", '%' . $wpdb->esc_like( $meta['thumb'] ) . '%', $post_id)) ) {
-			$thumbfile = str_replace(basename($file), $meta['thumb'], $file);
-			/** This filter is documented in wp-includes/functions.php */
-			$thumbfile = apply_filters( 'wp_delete_file', $thumbfile );
-			@ unlink( path_join($uploadpath['basedir'], $thumbfile) );
+		if ( ! $wpdb->get_row( $wpdb->prepare( "SELECT meta_id FROM $wpdb->postmeta WHERE meta_key = '_wp_attachment_metadata' AND meta_value LIKE %s AND post_id <> %d", '%' . $wpdb->esc_like( $meta['thumb'] ) . '%', $post_id ) ) ) {
+			$thumbfile = str_replace( basename( $file ), $meta['thumb'], $file );
+			if ( ! empty( $thumbfile ) ) {
+				$thumbfile = path_join( $uploadpath['basedir'], $thumbfile );
+				$thumbdir  = path_join( $uploadpath['basedir'], dirname( $file ) );
+
+				if ( ! wp_delete_file_from_directory( $thumbfile, $thumbdir ) ) {
+					$deleted = false;
+				}
+			}
 		}
 	}
 
 	// Remove intermediate and backup images if there are any.
 	if ( isset( $meta['sizes'] ) && is_array( $meta['sizes'] ) ) {
+		$intermediate_dir = path_join( $uploadpath['basedir'], dirname( $file ) );
 		foreach ( $meta['sizes'] as $size => $sizeinfo ) {
 			$intermediate_file = str_replace( basename( $file ), $sizeinfo['file'], $file );
-			/** This filter is documented in wp-includes/functions.php */
-			$intermediate_file = apply_filters( 'wp_delete_file', $intermediate_file );
-			@ unlink( path_join( $uploadpath['basedir'], $intermediate_file ) );
+			if ( ! empty( $intermediate_file ) ) {
+				$intermediate_file = path_join( $uploadpath['basedir'], $intermediate_file );
+
+				if ( ! wp_delete_file_from_directory( $intermediate_file, $intermediate_dir ) ) {
+					$deleted = false;
+				}
+			}
 		}
 	}
 
-	if ( is_array($backup_sizes) ) {
+	if ( is_array( $backup_sizes ) ) {
+		$del_dir = path_join( $uploadpath['basedir'], dirname( $meta['file'] ) );
 		foreach ( $backup_sizes as $size ) {
-			$del_file = path_join( dirname($meta['file']), $size['file'] );
-			/** This filter is documented in wp-includes/functions.php */
-			$del_file = apply_filters( 'wp_delete_file', $del_file );
-			@ unlink( path_join($uploadpath['basedir'], $del_file) );
+			$del_file = path_join( dirname( $meta['file'] ), $size['file'] );
+			if ( ! empty( $del_file ) ) {
+				$del_file = path_join( $uploadpath['basedir'], $del_file );
+
+				if ( ! wp_delete_file_from_directory( $del_file, $del_dir ) ) {
+					$deleted = false;
+				}
+			}
 		}
 	}
 
-	wp_delete_file( $file );
+	if ( ! wp_delete_file_from_directory( $file, $uploadpath['basedir'] ) ) {
+		$deleted = false;
+	}
 
-	clean_post_cache( $post );
-
-	return $post;
+	return $deleted;
 }
 
 /**