hardMultiple ChoiceObjective-mapped
CAS-004 Practice Question: The engineer needs to prevent brute-force attacks…
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?
Answer choices
Why each option matters
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.
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.
- ✗
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CAS-005 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-005 exam.