An attacker used XSS to compromise a web server.

Comprehensive and Detailed In-Depth Explanation:

AWeb Application Firewall (WAF)is designed toprotect web applications from attackssuch asCross-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.

AWAF is the best solutionfor protecting web servers fromXSS, SQL injection, and other web-based threats.