The answer is the mismatch between the Received header and the DKIM-Signature domain, because the Received header reveals the email physically originated from mail.attacker.com, not from legitbank.com’s own mail servers, which is a definitive indicator of email spoofing. While DKIM-Signature includes d=legitbank.com to claim the sender’s domain, the actual routing path in the Received header exposes the true source, and a failed DKIM verification would further confirm tampering. On the CHFI exam, this tests your ability to correlate header fields during forensic email analysis—a common trap is focusing only on the DKIM or From field while ignoring the Received chain. Remember the memory tip: “Follow the mail path, not the signature’s claim.”
CHFI Application, Email and Cloud Forensics Practice Question
This CHFI practice question tests your understanding of application, email and cloud forensics. 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 an investigation, an analyst extracts email headers from a suspicious email. The header includes: Received: from mail.attacker.com (192.168.1.100); DKIM-Signature: v=1; a=rsa-sha256; d=legitbank.com; s=selector1; bh=...; The email claims to be from support@legitbank.com. Which indicator strongly suggests email spoofing?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Received header shows the email came from a server not owned by legitbank.com
The DKIM-Signature domain (d=legitbank.com) should match the sender domain. However, the Received header shows the email originated from mail.attacker.com, not legitbank.com's mail servers. Additionally, analyzing the DKIM signature might fail if it doesn't match, but the mismatch in origin is a clear spoofing indicator.
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.
✗
The email was sent on a weekend
Why it's wrong here
The day of week is not a reliable spoofing indicator.
✗
The DKIM signature uses RSA-SHA256 algorithm
Why it's wrong here
RSA-SHA256 is a common and legitimate DKIM algorithm.
✗
The X-Originating-IP header is present
Why it's wrong here
X-Originating-IP is often present in legitimate emails and doesn't indicate spoofing by itself.
✓
The Received header shows the email came from a server not owned by legitbank.com
Why this is correct
Legitimate emails from legitbank.com would originate from their own mail servers, not attacker.com.
Related concept
Static NAT maps one inside address to one outside address.
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.
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 CHFI 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 CHFI NAT questions on configuration and troubleshooting.
Application, Email and Cloud Forensics — This question tests Application, Email and Cloud Forensics — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The Received header shows the email came from a server not owned by legitbank.com — The DKIM-Signature domain (d=legitbank.com) should match the sender domain. However, the Received header shows the email originated from mail.attacker.com, not legitbank.com's mail servers. Additionally, analyzing the DKIM signature might fail if it doesn't match, but the mismatch in origin is a clear spoofing indicator.
What should I do if I get this CHFI 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 CHFI 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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