The answer is a potential SMB exploitation attempt from an external host. This is correct because the firewall log shows a TCP SYN packet originating from a high source port and destined for port 445, which is the standard port for Server Message Block (SMB) services. In SMB exploitation detection, an unsolicited inbound SYN to port 445 from an external IP is a classic indicator of a reconnaissance or attack attempt, most famously associated with the EternalBlue exploit used in ransomware like WannaCry. On the ISC2 Certified in Cybersecurity CC exam, this scenario tests your ability to recognize common attack vectors by analyzing basic network logs; a common trap is confusing port 445 with file-sharing ports like 139 or assuming all inbound SYN packets are benign. Remember the memory tip: “Port 445 from outside? An exploit may be trying to hide.”
ISC2 CC Security Principles Practice Question
This CC practice question tests your understanding of security principles. 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.
Exhibit
Refer to the exhibit.
```
Jul 15 09:32:17 firewall kernel: [429493.77] IN=eth0 OUT= MAC=00:1a:2b:3c:4d:5e:00:11:22:33:44:55:08:00 SRC=203.0.113.5 DST=198.51.100.20 LEN=40 TOS=0x00 PREC=0x00 TTL=64 ID=54321 PROTO=TCP SPT=44523 DPT=445 WINDOW=1024 RES=0x00 SYN URGP=0
```
A security analyst reviews this firewall log entry. What type of activity is most likely being attempted?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A potential SMB exploitation attempt from an external host.
The log shows a TCP SYN packet from a high source port to destination port 445 (SMB), commonly used in ransomware attacks like EternalBlue.
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.
✗
A legitimate SMB file sharing connection from an internal client.
Why it's wrong here
The source IP is external (203.0.113.5) and the destination is internal (198.51.100.20), indicating an inbound connection attempt.
✓
A potential SMB exploitation attempt from an external host.
Why this is correct
The SYN packet to port 445 from an external source is typical of SMB exploits such as EternalBlue.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
A port scan attempt on port 445.
Why it's wrong here
A single SYN packet does not indicate a scan; scans usually have multiple packets.
✗
An outbound connection to an SMB server.
Why it's wrong here
The destination is internal, so it's inbound, not outbound.
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 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CC 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 CC NAT questions on configuration and troubleshooting.
Security Principles — This question tests Security Principles — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: A potential SMB exploitation attempt from an external host. — The log shows a TCP SYN packet from a high source port to destination port 445 (SMB), commonly used in ransomware attacks like EternalBlue.
What should I do if I get this CC 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 CC NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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