- A
Set the User-Agent to: <img src=x onerror=alert(1)>
Why wrong: While this is also a valid XSS payload, option A is more straightforward for a test. However, both could work. The question asks for 'MOST effective' and simple script is classic. But note: many XSS filters block <script> tags, so <img> might be better. However, the context of User-Agent is usually reflected in the response body and <script> works. To be safe, <script> is standard. But <img> is also valid. Since the instruction says 'MOST effective', both are effective but <script> is simpler. I'll keep A as correct.
- B
Set the User-Agent to: ' OR '1'='1
Why wrong: This is a SQL injection payload, not XSS.
- C
Set the User-Agent to: <script>alert('XSS')</script>
This payload will execute JavaScript if the User-Agent is reflected unsanitized, proving the vulnerability.
- D
Set the User-Agent to: ../../../../etc/passwd
Why wrong: This is a directory traversal payload, not XSS.
Quick Answer
The answer is to set the User-Agent header to <script>alert('XSS')</script>. This payload is the most effective proof of concept because it immediately demonstrates a reflected XSS vulnerability by causing the browser to execute JavaScript in the victim’s session, confirming that user-supplied input is echoed back without sanitization. On the Certified Ethical Hacker CEH exam, this scenario tests your ability to identify injection points in HTTP headers, a common blind spot where testers focus only on URL parameters. A frequent trap is overcomplicating the payload with obfuscation or event handlers, but the simplest alert script is the fastest way to validate the flaw in a single request. Remember the memory tip: “Reflect the header, alert the tester”—if the header value appears in the response, a basic script tag is all you need to confirm the risk.
CEH Web Application and Injection Attacks Practice Question
This CEH practice question tests your understanding of web application and injection attacks. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
During a security assessment, a tester discovers an endpoint that reflects the 'User-Agent' header in the response without sanitization. The tester wants to confirm a reflected XSS vulnerability. Which of the following payloads would be MOST effective to demonstrate the issue in a single request?
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
Set the User-Agent to: <script>alert('XSS')</script>
Using a simple script alert like <script>alert(1)</script> is a standard proof-of-concept for reflected XSS. The exact payload may vary, but it must execute JavaScript. The simplest is an alert.
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.
- ✗
Set the User-Agent to: <img src=x onerror=alert(1)>
Why it's wrong here
While this is also a valid XSS payload, option A is more straightforward for a test. However, both could work. The question asks for 'MOST effective' and simple script is classic. But note: many XSS filters block <script> tags, so <img> might be better. However, the context of User-Agent is usually reflected in the response body and <script> works. To be safe, <script> is standard. But <img> is also valid. Since the instruction says 'MOST effective', both are effective but <script> is simpler. I'll keep A as correct.
- ✗
Set the User-Agent to: ' OR '1'='1
Why it's wrong here
This is a SQL injection payload, not XSS.
- ✓
Set the User-Agent to: <script>alert('XSS')</script>
Why this is correct
This payload will execute JavaScript if the User-Agent is reflected unsanitized, proving the vulnerability.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Set the User-Agent to: ../../../../etc/passwd
Why it's wrong here
This is a directory traversal payload, not XSS.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 practitioner preparing for the CEH exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which CEH exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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Web Application and Injection Attacks — study guide chapter
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FAQ
Questions learners often ask
What does this CEH question test?
Web Application and Injection Attacks — This question tests Web Application and Injection Attacks — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Set the User-Agent to: <script>alert('XSS')</script> — Using a simple script alert like <script>alert(1)</script> is a standard proof-of-concept for reflected XSS. The exact payload may vary, but it must execute JavaScript. The simplest is an alert.
What should I do if I get this CEH question wrong?
Identify which CEH exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on CEH
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An attacker intercepts a request and notices that the server reflects the value of the 'User-Agent' header in the response without sanitization. The attacker crafts a payload that triggers an alert box. This is an example of:
hard- A.HTTP header injection
- B.DOM-based XSS
- C.Stored XSS
- ✓ D.Reflected XSS
Why D: Reflected XSS occurs when the application immediately returns the user input in the response; here, the User-Agent header is reflected.
Last reviewed: Jun 21, 2026
This CEH practice question is part of Courseiva's free EC-Council 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 CEH exam.
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