The answer is directory traversal and unrestricted file upload. This exploit succeeds because the application fails to sanitize the file name, allowing the attacker to use "../" sequences to navigate up the directory structure, while simultaneously lacking any validation on file type or content, enabling the upload of a malicious PHP shell. On the Certified Ethical Hacker CEH exam, this scenario tests your understanding of how two low-severity flaws combine into a critical remote code execution (RCE) risk—a common theme in the web application penetration testing domain. A frequent trap is assuming file upload alone is the issue, but the traversal component is what places the shell outside the intended upload directory. Memory tip: think of it as “path escape plus payload drop”—if the app lets you name your file with dots and slashes, and doesn’t check what you’re uploading, you’ve got a one-two punch for RCE.
CEH Web Application and Injection Attacks Practice Question
This CEH practice question tests your understanding of web application and injection attacks. 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 penetration tester finds that a web application allows uploading a file with the name '../../var/www/html/shell.php'. The file is successfully written to the server. Which combination of vulnerabilities does this exploit?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Directory traversal and unrestricted file upload
Directory traversal allows moving up directories, and unrestricted file upload allows writing a PHP shell, leading to remote code execution.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Cross-Site Scripting (XSS) and CSRF
Why it's wrong here
XSS and CSRF are client-side attacks, not related to file upload.
✗
Local File Inclusion (LFI) and Remote File Inclusion (RFI)
Why it's wrong here
LFI/RFI involve including files, not uploading them.
✓
Directory traversal and unrestricted file upload
Why this is correct
The traversal path in the filename exploits directory traversal, and the ability to upload a PHP file indicates unrestricted file upload.
Related concept
Static NAT maps one inside address to one outside address.
✗
SQL injection and command injection
Why it's wrong here
No SQL or command injection is evident.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Trap categories for this question
Command / output trap
No SQL or command injection is evident.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CEH question in full detail.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CEH NAT questions on configuration and troubleshooting.
Web Application and Injection Attacks — This question tests Web Application and Injection Attacks — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Directory traversal and unrestricted file upload — Directory traversal allows moving up directories, and unrestricted file upload allows writing a PHP shell, leading to remote code execution.
What should I do if I get this CEH question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CEH NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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