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 accepts XML input and returns the parsed data in the response. The tester submits the following payload: <?xml version="1.0"?><!DOCTYPE foo [<!ENTITY xxe SYSTEM "file:///etc/passwd">]><root>&xxe;</root>. The server returns the contents of /etc/passwd. Which vulnerability is being exploited?
SSRF
Why wrong: SSRF involves server-side request forgery to internal systems, not XML parsing.
Command injection
Why wrong: Command injection would execute OS commands, not read files via XML entities.
XXE injection
The payload uses an external entity to read a file, which is XXE.
XPath injection
Why wrong: XPath injection targets XPath queries, not XML entity parsing.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
XXE injection
The payload defines an external entity (XXE) that reads a local file, indicating an XML External Entity (XXE) injection vulnerability.
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
For each option: why learners choose it and why it is or isn't the right answer here.
SSRF
Why it's wrong here
SSRF involves server-side request forgery to internal systems, not XML parsing.
Command injection
Why it's wrong here
Command injection would execute OS commands, not read files via XML entities.
XXE injection
Why this is correct
The payload uses an external entity to read a file, which is XXE.
Related concept
Static NAT maps one inside address to one outside address.
XPath injection
Why it's wrong here
XPath injection targets XPath queries, not XML entity parsing.
Common exam traps
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
Command injection would execute OS commands, not read files via XML entities.
Detailed technical explanation
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.
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
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.
What to study next
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.
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FAQ
Web Application and Injection Attacks — This question tests Web Application and Injection Attacks — Static NAT maps one inside address to one outside address..
The correct answer is: XXE injection — The payload defines an external entity (XXE) that reads a local file, indicating an XML External Entity (XXE) injection vulnerability.
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.
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 21, 2026
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