Which techniques should address XSS vulnerabilities?

Which techniques should address XSS vulnerabilities?

• A. Validating all params before inclusion and utilizing context-sensitive escaping.
• B. Rely on client-side validation
• C. Use of inline scripts without validation
• D. Disable all escaping

Answer: (A)

Cross-site scripting is prevented by treating user input as untrusted and handling it safely at output time. The best defense is to validate inputs and then render them with context-sensitive escaping. Validating all parameters before inclusion helps ensure data fits expected formats and reduces the chance that unsafe data slips through. Once data is validated, escaping it appropriately for the specific place it will appear—whether in HTML content, an HTML attribute, a JavaScript string, a URL, or CSS—prevents the browser from interpreting it as code. For example, in HTML text you escape characters like <, >, &, and quotes; in a JavaScript string you also escape backslashes and quotes; in a URL you percent-encode unsafe characters. This layered approach guards against injections even if some input wasn’t perfectly sanitized upstream, and it remains effective even when parts of the system try to bypass client-side checks. Relying only on client-side validation can be bypassed by attackers, while placing inline scripts without validation is inherently dangerous, and disabling escaping would expose the page to easily injected scripts.

Cross-site scripting is prevented by treating user input as untrusted and handling it safely at output time. The best defense is to validate inputs and then render them with context-sensitive escaping. Validating all parameters before inclusion helps ensure data fits expected formats and reduces the chance that unsafe data slips through. Once data is validated, escaping it appropriately for the specific place it will appear—whether in HTML content, an HTML attribute, a JavaScript string, a URL, or CSS—prevents the browser from interpreting it as code. For example, in HTML text you escape characters like <, >, &, and quotes; in a JavaScript string you also escape backslashes and quotes; in a URL you percent-encode unsafe characters. This layered approach guards against injections even if some input wasn’t perfectly sanitized upstream, and it remains effective even when parts of the system try to bypass client-side checks. Relying only on client-side validation can be bypassed by attackers, while placing inline scripts without validation is inherently dangerous, and disabling escaping would expose the page to easily injected scripts.