The correct answer is that an attacker can submit malicious data directly to the server without client-side constraints. This is the core risk of client-side only input validation because all validation logic executed in the browser—whether via JavaScript or HTML attributes—is fully under the attacker’s control. By intercepting the request or crafting a raw HTTP POST, an attacker bypasses the client entirely and sends crafted payloads straight to the server, which then processes unvalidated input. On the CISSP exam, this concept tests your understanding of the defense-in-depth principle and the distinction between security controls and usability features; a common trap is confusing client-side validation with a security measure when it is actually a convenience for users. Remember the memory tip: “Client-side is for the user, server-side is for security.”
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 security assessment reveals that a web application uses client-side input validation exclusively. What is the most likely security risk?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An attacker can submit malicious data directly to the server without client-side constraints.
Option A is correct because client-side validation is easily bypassed by an attacker who sends requests directly to the server. Option B is wrong because usability is not a security risk. Option C is wrong while client-side can be tampered; the core risk is missing server-side validation. Option D is wrong because XSS is typically mitigated by output encoding, not input validation.
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.
✗
Attacker can inject malicious scripts that execute on the client side.
Why it's wrong here
XSS is typically due to lack of output encoding, not input validation.
✓
An attacker can submit malicious data directly to the server without client-side constraints.
Why this is correct
Client-side validation only works in the browser; server-side validation is necessary to prevent malicious input.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The application will have poor user experience due to slow responses.
Why it's wrong here
Client-side validation can improve user experience, not degrade it.
✗
The client-side code can be obfuscated but not decrypted.
Why it's wrong here
Obfuscation can be reversed but the main risk is bypassing validation.
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.
Trap categories for this question
Command / output trap
XSS is typically due to lack of output encoding, not input validation.
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 SOC analyst notices unusual lateral movement in the network at 2 AM. The IR playbook dictates: identify and contain (isolate the affected machine), then eradicate (remove the malware), then recover (restore from backup), then document. Skipping containment before eradication risks the attacker regaining access. Questions like this test the sequence and rationale of incident response phases.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Identify which CISSP 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.
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: An attacker can submit malicious data directly to the server without client-side constraints. — Option A is correct because client-side validation is easily bypassed by an attacker who sends requests directly to the server. Option B is wrong because usability is not a security risk. Option C is wrong while client-side can be tampered; the core risk is missing server-side validation. Option D is wrong because XSS is typically mitigated by output encoding, not input validation.
What should I do if I get this CISSP question wrong?
Identify which CISSP 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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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