diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index 979536f751..7db3bbafd9 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -1923,6 +1923,11 @@ 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 ) {