The answer is implementing fail2ban with a threshold of 5 attempts per minute, as this is the most effective security control to prevent brute-force attacks on SSH while preserving legitimate access. Fail2ban works by monitoring authentication logs for repeated failed login attempts and dynamically updating firewall rules to block the offending IP address after a configurable threshold, stopping brute-force attacks in real time without affecting authorized users like 10.0.0.50. On the CompTIA SecurityX CAS-004 exam, this question tests your ability to distinguish between active, adaptive controls and weaker alternatives such as security by obscurity or static whitelisting. A common trap is choosing to disable root login or change the SSH port, but those measures do not address brute-force attempts against other user accounts. Remember the memory tip: “Fail2ban fails the brute, not the user”—it adapts to attack patterns while keeping the door open for legitimate connections.
CAS-004 Security Engineering Practice Question
This CAS-004 practice question tests your understanding of security engineering. 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.
Aug 15 14:23:10 server1 sshd[1234]: Failed password for root from 192.168.1.200 port 56789 ssh2
Aug 15 14:23:12 server1 sshd[1234]: Failed password for root from 192.168.1.200 port 56790 ssh2
Aug 15 14:23:15 server1 sshd[1234]: Failed password for root from 192.168.1.200 port 56791 ssh2
...
Aug 15 14:25:30 server1 sshd[1234]: Accepted password for admin from 10.0.0.50 port 34821 ssh2
The engineer needs to prevent brute-force attacks while allowing legitimate access. Which security control is MOST effective?
Refer to the exhibit.
Aug 15 14:23:10 server1 sshd[1234]: Failed password for root from 192.168.1.200 port 56789 ssh2
Aug 15 14:23:12 server1 sshd[1234]: Failed password for root from 192.168.1.200 port 56790 ssh2
Aug 15 14:23:15 server1 sshd[1234]: Failed password for root from 192.168.1.200 port 56791 ssh2
...
Aug 15 14:25:30 server1 sshd[1234]: Accepted password for admin from 10.0.0.50 port 34821 ssh2
A
Disable root login
Why wrong: Disabling root login reduces risk but does not prevent brute-force attacks on other usernames.
B
Change SSH port to 2222
Why wrong: Changing the port is easily discovered by port scanning and provides no real security.
C
Implement fail2ban with a threshold of 5 attempts per minute
Fail2ban automatically blocks offending IPs after exceeding the threshold, allowing legitimate traffic.
D
Implement IP whitelist for 10.0.0.0/8
Why wrong: IP whitelisting is too restrictive and would block legitimate remote users from other subnets.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Implement fail2ban with a threshold of 5 attempts per minute
Fail2ban dynamically blocks IP addresses after a configurable number of failed attempts, stopping brute-force while allowing legitimate users (e.g., 10.0.0.50) to connect. Disabling root login only prevents root access but not attacks on other users. Changing the SSH port is security by obscurity. IP whitelisting for 10.0.0.0/8 would block all other legitimate users and is not flexible.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Disable root login
Why it's wrong here
Disabling root login reduces risk but does not prevent brute-force attacks on other usernames.
✗
Change SSH port to 2222
Why it's wrong here
Changing the port is easily discovered by port scanning and provides no real security.
✓
Implement fail2ban with a threshold of 5 attempts per minute
Why this is correct
Fail2ban automatically blocks offending IPs after exceeding the threshold, allowing legitimate traffic.
Related concept
Read the scenario before looking for a memorised answer.
✗
Implement IP whitelist for 10.0.0.0/8
Why it's wrong here
IP whitelisting is too restrictive and would block legitimate remote users from other subnets.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the CAS-004 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which CAS-004 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Security Engineering — This question tests Security Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Implement fail2ban with a threshold of 5 attempts per minute — Fail2ban dynamically blocks IP addresses after a configurable number of failed attempts, stopping brute-force while allowing legitimate users (e.g., 10.0.0.50) to connect. Disabling root login only prevents root access but not attacks on other users. Changing the SSH port is security by obscurity. IP whitelisting for 10.0.0.0/8 would block all other legitimate users and is not flexible.
What should I do if I get this CAS-004 question wrong?
Identify which CAS-004 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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