This CISA practice question tests your understanding of information systems acquisition, development and implementation. 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 company is integrating a third-party payment gateway into its e-commerce platform. Which of the following is the MOST important security control to implement?
Implement role-based access control
Why wrong: Important but addresses internal access.
Log all transactions
Why wrong: Detective control, not preventive.
Validate all input from the payment gateway
Prevents injection and data corruption.
Encrypt all data with SSL
Why wrong: Important but not the most important for integration.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Validate all input from the payment gateway
Option C is correct because input validation from the payment gateway is the most critical security control. The payment gateway returns data (e.g., transaction status, amount, token) that is consumed by the e-commerce platform. Without strict validation, an attacker could inject malicious payloads (e.g., SQL injection, XSS) via manipulated gateway responses, leading to data breaches or unauthorized transactions. This control directly prevents injection attacks at the integration boundary.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Implement role-based access control
Why it's wrong here
Important but addresses internal access.
Log all transactions
Why it's wrong here
Detective control, not preventive.
Validate all input from the payment gateway
Why this is correct
Prevents injection and data corruption.
Related concept
Read the scenario before looking for a memorised answer.
Encrypt all data with SSL
Why it's wrong here
Important but not the most important for integration.
Common exam traps
The trap here is that candidates often choose encryption (SSL/TLS) as the most important control because it is a well-known security measure, but they overlook that encryption does not validate the trustworthiness of the decrypted data, which is the primary risk when integrating with an external system.
Detailed technical explanation
Input validation should include both syntactic checks (e.g., ensuring a transaction amount is a positive number within expected bounds) and semantic checks (e.g., verifying that a returned status code matches expected values per the payment gateway's API specification). A real-world scenario is the 2019 Capital One breach, where a misconfigured web application firewall (WAF) failed to validate input from a third-party service, allowing SSRF attacks. Under the hood, this often involves validating JSON or XML responses against a strict schema (e.g., using JSON Schema or XSD) and sanitizing any data that will be reflected in web pages or database queries.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the CISA 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
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FAQ
Information Systems Acquisition, Development and Implementation — This question tests Information Systems Acquisition, Development and Implementation — Read the scenario before looking for a memorised answer..
The correct answer is: Validate all input from the payment gateway — Option C is correct because input validation from the payment gateway is the most critical security control. The payment gateway returns data (e.g., transaction status, amount, token) that is consumed by the e-commerce platform. Without strict validation, an attacker could inject malicious payloads (e.g., SQL injection, XSS) via manipulated gateway responses, leading to data breaches or unauthorized transactions. This control directly prevents injection attacks at the integration boundary.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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