You are on your company's development team.

Use Cloud IAP based on IP address or end-user device attributes to prevent and fix the vulnerability.

Set up an HTTPS load balancer, and then use Cloud Armor for the production environment to prevent the potential XSS attack.

Use Web Security Scanner to validate the usage of an outdated library in the code, and then use a secured version of the included library.

Use Web Security Scanner in staging to simulate an XSS injection attack, and then use a templating system that supports contextual auto-escaping.