Comprehensive and Detailed In-Depth Explanation:
A Web Application Firewall (WAF) is designed to protect web applications from attacks such as Cross- Site Scripting (XSS) by filtering and monitoring HTTP traffic between the internet and a web application.
* Next-Generation Firewalls (NGFW) (A) provide advanced network security but are not specifically designed to protect web applications from XSS attacks.
* Unified Threat Management (UTM) (B) provides multiple security functions but lacks the specialized application-layer protection needed to mitigate XSS.
* Network Access Control (NAC) (D) controls device access to the network but does not prevent web- based attacks.
A WAF is the best solution for protecting web servers from XSS, SQL injection, and other web-based threats.