The answer is to add the external IP address to the firewall deny list and implement an IP allowlist for SSH access. This is correct because the attack is a classic brute-force or password-spraying attempt originating from a single external source; blocking that IP at the network layer immediately stops all malicious traffic, while an allowlist ensures only pre-approved, trusted IPs can even reach the SSH service, effectively neutralizing the attack regardless of password strength or authentication method. On the CompTIA SecurityX CAS-004 exam, this scenario tests your understanding of network-layer access controls versus host-based defenses—a common trap is choosing account lockout policies, which are reactive and can cause denial of service, whereas a firewall deny and allowlist is proactive and surgically precise. Remember the memory tip: “Block the bad, allow the good—firewall rules stop brute force where it should.”
CAS-004 Security Operations Practice Question
This CAS-004 practice question tests your understanding of security operations. 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 SOC analyst is reviewing a large volume of failed login attempts across multiple user accounts from a single external IP address. The attempts use common usernames and passwords over SSH (port 22). Which security control would be most effective at preventing this type of attack?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add the external IP address to the firewall deny list and implement an IP allowlist for SSH access.
Option D is correct because the attack is a brute-force or password-spraying attempt from a single external IP. Adding that IP to a firewall deny list immediately blocks all traffic from that source, while implementing an IP allowlist for SSH access ensures only trusted IPs can reach the service. This directly prevents the attack at the network layer, regardless of password strength or authentication method.
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.
✗
Enforce a minimum password complexity policy for all users.
Why it's wrong here
Password complexity reduces the chance of successful authentication but does not prevent the attack.
✗
Require multi-factor authentication for all SSH logins.
Why it's wrong here
MFA prevents successful authentication but the attack still generates logs and resource usage.
✗
Implement rate limiting on SSH connections per source IP.
Why it's wrong here
Rate limiting slows down but does not stop a determined attacker; the source IP can still attempt logins.
✓
Add the external IP address to the firewall deny list and implement an IP allowlist for SSH access.
Why this is correct
This immediately blocks the attack and prevents any further attempts from that IP.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose rate limiting (Option C) because it seems like a direct mitigation, but they fail to realize that rate limiting only slows the attack, whereas blocking the IP and using an allowlist stops it entirely.
Detailed technical explanation
How to think about this question
In practice, an IP allowlist for SSH (e.g., using iptables or a cloud security group) restricts access to only known management IPs, making the attack impossible from any other source. Firewall deny lists are reactive but effective when the attacker IP is identified; combining both provides defense in depth. This aligns with the principle of least privilege and is a common recommendation in the NIST SP 800-53 AC-3 (Access Enforcement) control.
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.
TExam Day Tips
→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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Operations — This question tests Security Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add the external IP address to the firewall deny list and implement an IP allowlist for SSH access. — Option D is correct because the attack is a brute-force or password-spraying attempt from a single external IP. Adding that IP to a firewall deny list immediately blocks all traffic from that source, while implementing an IP allowlist for SSH access ensures only trusted IPs can reach the service. This directly prevents the attack at the network layer, regardless of password strength or authentication method.
What should I do if I get this CAS-004 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Based on the auth.log exhibit, what is the MOST appropriate immediate action to mitigate this attack?
easy
A.Disable root login and remove the admin account.
B.Block the entire 192.168.1.0/24 subnet at the firewall.
✓ C.Configure fail2ban to block the IP address after a threshold of failed attempts.
D.Change the SSH port to a non-standard port.
Why C: Option C is correct. The log shows a brute-force attack against SSH. Installing fail2ban will dynamically block the IP after multiple failures. Option A is too broad and may block legitimate users from that subnet. Option B doesn't address the immediate attack. Option D is good practice but does not stop the ongoing attack immediately.
Last reviewed: Jun 11, 2026
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This CAS-004 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CAS-004 exam.
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