- A
Use Content Security Policy (CSP) headers to restrict script execution
Why wrong: CSP is a defense-in-depth measure but not sufficient alone.
- B
Sanitize input by removing all HTML tags before storing
Why wrong: Removing tags may break functionality; encoding is more reliable.
- C
Apply output encoding based on the context (e.g., HTML entity encoding)
Context-aware encoding prevents script execution.
- D
Store comments in a separate domain to isolate them
Why wrong: Isolation does not prevent XSS; it only limits impact.
Question 664 of 1,000
CISSP Software Development Security Practice Question
This CISSP practice question tests your understanding of software development security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A development team is fixing a stored cross-site scripting (XSS) vulnerability in a web application that displays user comments. The application stores comments in a database and renders them in HTML. Which of the following is the most secure approach to prevent XSS?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Apply output encoding based on the context (e.g., HTML entity encoding)
Output encoding (C) is the most secure approach because it neutralizes malicious scripts at the point of rendering, ensuring that user-controlled data is treated as text rather than executable code. For HTML contexts, HTML entity encoding (e.g., `<script>`) prevents the browser from interpreting injected tags, regardless of how the data was stored. This aligns with the defense-in-depth principle and is the primary mitigation for stored XSS as recommended by OWASP.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use Content Security Policy (CSP) headers to restrict script execution
Why it's wrong here
CSP is a defense-in-depth measure but not sufficient alone.
- ✗
Sanitize input by removing all HTML tags before storing
Why it's wrong here
Removing tags may break functionality; encoding is more reliable.
- ✓
Apply output encoding based on the context (e.g., HTML entity encoding)
Why this is correct
Context-aware encoding prevents script execution.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Store comments in a separate domain to isolate them
Why it's wrong here
Isolation does not prevent XSS; it only limits impact.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that input sanitization (removing tags) is the best approach, but the CISSP emphasizes that output encoding is the definitive control because it works regardless of how data enters the system and preserves data integrity for legitimate use.
Detailed technical explanation
How to think about this question
Output encoding must be context-aware: HTML entity encoding works for HTML body contexts, but attribute contexts require attribute-specific encoding (e.g., `"` for double quotes), and JavaScript contexts require JavaScript escaping (e.g., `\x3C`). A common subtlety is that using `innerHTML` in JavaScript bypasses server-side encoding, so client-side rendering must also apply encoding. In real-world scenarios, frameworks like React automatically encode output by default, but raw `dangerouslySetInnerHTML` can reintroduce XSS if used carelessly.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this CISSP question test?
Software Development Security — This question tests Software Development Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Apply output encoding based on the context (e.g., HTML entity encoding) — Output encoding (C) is the most secure approach because it neutralizes malicious scripts at the point of rendering, ensuring that user-controlled data is treated as text rather than executable code. For HTML contexts, HTML entity encoding (e.g., `<script>`) prevents the browser from interpreting injected tags, regardless of how the data was stored. This aligns with the defense-in-depth principle and is the primary mitigation for stored XSS as recommended by OWASP.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jul 4, 2026
This CISSP practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CISSP exam.
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