Filesystem API: Prevent directory travelersals when creating new folders.

Reject file paths that contain sub-directory paths.

Backports [46476] to the 5.2 branch.

Props iandunn, xknown, sstoqnov, whyisjake.

Built from https://develop.svn.wordpress.org/branches/5.2@46482


git-svn-id: http://core.svn.wordpress.org/branches/5.2@46280 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/functions.php

@@ -1787,6 +1787,11 @@ function wp_mkdir_p( $target ) {
 		return @is_dir( $target );
 	}
 
+	// Do not allow path traversals.
+	if ( false !== strpos( $target, '../' ) || false !== strpos( $target, '..' . DIRECTORY_SEPARATOR ) ) {
+		return false;
+	}
+
 	// We need to find the permissions of the parent folder that exists and inherit that.
 	$target_parent = dirname( $target );
 	while ( '.' != $target_parent && ! is_dir( $target_parent ) && dirname( $target_parent ) !== $target_parent ) {

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.2.4-alpha-46481';
+$wp_version = '5.2.4-alpha-46482';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.