Which security device is designed to prevent cross-site scripting and SQL injection by inspecting and filtering HTTP traffic?

• A. Proxy Server
• B. Reverse Proxy
• C. Web Application Firewall (WAF)
• D. NIDS

Answer: (C)

Web application protection centers on inspecting HTTP traffic for malicious payloads. Cross-site scripting and SQL injection exploit data in headers, query strings, and the body of requests, so a Web Application Firewall is built to analyze that data at the application layer and enforce security rules. It sits in line with the web server (often as a reverse proxy or cloud service) and can block, modify, or sanitize requests that match known attack patterns or exhibit suspicious behavior. By applying signatures, anomaly detection, and strict input validation rules, a WAF stops attacks before they reach the application, preserving both availability and data integrity.

A proxy server mainly forwards traffic and may perform basic filtering or caching, but it isn’t inherently focused on detecting and blocking web-app-specific exploits. A reverse proxy provides front-end access and load balancing for web servers and can host security features, but the key protective capability against XSS and SQL injection comes from the WAF. A network-based intrusion detection system monitors traffic for signs of intrusion and alerts, but it typically does not enforce the same level of application-layer blocking to prevent specific web app attacks.