An administrator discovers a cross-site scripting vulnerability on a company website.

Cross-site scripting (XSS) occurs when a web application fails to properly validate or sanitize user input, allowing attackers to inject malicious scripts into web pages viewed by other users. The most effective remediation is input validation, which ensures that only safe, expected data is accepted by the application.

Security+ SY0-701 highlights input validation as a primary defense against:

XSS

SQL injection

Command injection

Path traversal attacks

By validating and sanitizing input at both the client and server layers, organizations can strip harmful characters, block script tags, enforce strict data types, and ensure proper encoding.

A NGFW (B) or WAF (D) can mitigate attacks by blocking malicious payloads, but they do not fix the root cause within the web application. A vulnerability scan (C) identifies the issue but does not remediate it.

Therefore, only input validation (A) directly resolves the underlying coding flaw responsible for XSS.