Quick Answer
The correct answer is to validate file extension and content type on the server side, as this directly prevents webshell upload through server-side validation. Without this control, an attacker can bypass client-side filters by crafting a file with a legitimate extension but containing executable PHP code, and server-side checks of both the extension and the actual MIME type magic bytes ensure that only expected, non-executable file types are accepted. On the Systems Security Certified Practitioner SSCP exam, this concept tests your understanding of secure file upload mechanisms and the principle that client-side validation is never sufficient for security. A common trap is to assume that disabling PHP execution in the upload directory or relying on a WAF is enough, but these are compensating controls that can be evaded. Memory tip: think “two gates” — extension and content type — both must be locked server-side to stop a webshell from slipping through.
This SSCP practice question tests your understanding of security operations and administration. 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.
During a security assessment, a penetration tester discovers that a web application allows users to upload files without proper validation. The tester successfully uploads a PHP web shell. Which control would have MOST effectively prevented this exploitation?
Disable PHP execution in the upload directory.
Why wrong: This prevents execution but does not prevent uploading the file itself.
Implement a WAF rule to block common webshell patterns.
Why wrong: WAF can be bypassed with obfuscation.
Enable audit logging for file uploads.
Why wrong: Logging does not prevent the upload.
Validate file extension and content type on the server side.
Proper validation blocks malicious files at upload.
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 file extension and content type on the server side.
Option D is correct because server-side validation of both file extension and content type (e.g., MIME type magic bytes) is the most effective control to prevent uploading executable files like a PHP web shell. Without this validation, an attacker can bypass client-side checks and upload a malicious script that the server will execute. Disabling PHP execution in the upload directory (Option A) is a compensating control but does not prevent the upload itself, and a WAF rule (Option B) can be evaded with obfuscation or encoding.
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.
Disable PHP execution in the upload directory.
Why it's wrong here
This prevents execution but does not prevent uploading the file itself.
Implement a WAF rule to block common webshell patterns.
Why it's wrong here
WAF can be bypassed with obfuscation.
Enable audit logging for file uploads.
Why it's wrong here
Logging does not prevent the upload.
Validate file extension and content type on the server side.
Why this is correct
Proper validation blocks malicious files at upload.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often choose Option A (disabling PHP execution) because it seems like a direct fix, but the SSCP exam tests the principle that preventing the upload of malicious files (input validation) is more fundamental than mitigating execution after the fact.
Detailed technical explanation
Server-side file validation should check both the file extension (e.g., .php, .asp) and the actual content type by reading the file's magic bytes (e.g., the first few bytes of a PNG file are 89 50 4E 47). Attackers often use double extensions (e.g., shell.php.jpg) or null byte injection (e.g., shell.php%00.jpg) to bypass weak checks. In a real-world scenario, a missing validation allowed the 2017 Equifax breach where a vulnerable Apache Struts file upload component was exploited.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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Security Operations and Administration — study guide chapter
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FAQ
Security Operations and Administration — This question tests Security Operations and Administration — Read the scenario before looking for a memorised answer..
The correct answer is: Validate file extension and content type on the server side. — Option D is correct because server-side validation of both file extension and content type (e.g., MIME type magic bytes) is the most effective control to prevent uploading executable files like a PHP web shell. Without this validation, an attacker can bypass client-side checks and upload a malicious script that the server will execute. Disabling PHP execution in the upload directory (Option A) is a compensating control but does not prevent the upload itself, and a WAF rule (Option B) can be evaded with obfuscation or encoding.
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 25, 2026
This SSCP 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 SSCP exam.
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