Explanation
A WAF (web application firewall) is a type of firewall that protects web applications from common web-based attacks, such as SQL injection, cross-site scripting, and denial-of-service. A WAF can be deployed on the load balancer or on the web servers to filter and block malicious requests before they reach the application or the database. A WAF is the most likely option to improve the site security in this scenario, as it can prevent attacks that target the web application layer.
References:
Web Application Firewall (WAF) - AWS WAF, AWS Firewall Manager, and AWS Shield Advanced What is a Web Application Firewall (WAF)?
Web Application Firewall (WAF) - Oracle Cloud Infrastructure