WordPress SagePay Server Gateway for WooCommerce before 1.0.9 is vulnerable to cross-site scripting via the includes/pages/redirect.php page parameter.
View the template here CVE-2018-5316.yaml
References:
https://wordpress.org/support/topic/sagepay-server-gateway-for-woocommerce-1-0-7-cross-site-scripting/#post-9792337