Ticket #29696: 29696.patch

src/wp-includes/user.php

@@ -1679 +1679 @@
         if ( empty( $userdata['user_nicename'] ) ) {
                 $user_nicename = sanitize_title( $user_login );
         } else {
-                $user_nicename = $userdata['user_nicename'];
+                $sanitized_user_nicename = sanitize_user( $userdata['user_nicename'], true );
+                $user_nicename = sanitize_title( $sanitized_user_nicename );
         }
 
         // Store values to save in user meta.