Quick Answer
The correct answer is to configure SSH to use key-based authentication only, as this eliminates the risk of password-based attacks like brute-force or credential theft. By disabling password authentication and requiring a private key, you ensure that even if an attacker obtains a user’s password hash, they cannot log in because SSH keys are cryptographically bound to the client and never transmitted over the network. On the CompTIA Linux+ XK0-005 exam, this scenario tests your understanding of secure SSH configuration under Objective 3.2, often appearing as a “what should the admin do next” question where the trap is choosing to rotate passwords or enable fail2ban instead of disabling password auth entirely. A common memory tip is “keys, not secrets”—SSH keys replace shared secrets with asymmetric cryptography, so the server never sees a password to steal.
This XK0-005 practice question tests your understanding of security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 system administrator notices that an unauthorized user gained access to a server via SSH using a compromised user account. Which security measure should be implemented to prevent such attacks in the future?
Configure SSH to use key-based authentication only
Key-based authentication is more secure and prevents password attacks.
Disable SSH and use Telnet
Why wrong: Telnet is unencrypted and less secure.
Enforce a complex password policy
Why wrong: Complex passwords reduce brute force risk but do not prevent compromised passwords.
Allow all users to use sudo without passwords
Why wrong: This increases security risk.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Configure SSH to use key-based authentication only
Option A is correct because configuring SSH to use key-based authentication only eliminates the risk of password-based attacks, such as brute-force or credential theft. Since the compromised user account was accessed via SSH using a password, disabling password authentication and requiring a private key ensures that an attacker cannot log in even if they obtain the user's password hash. This aligns with the principle of least privilege and strong authentication, as SSH keys are cryptographically bound to the client and are not transmitted over the network.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Configure SSH to use key-based authentication only
Why this is correct
Key-based authentication is more secure and prevents password attacks.
Related concept
Read the scenario before looking for a memorised answer.
Disable SSH and use Telnet
Why it's wrong here
Telnet is unencrypted and less secure.
Enforce a complex password policy
Why it's wrong here
Complex passwords reduce brute force risk but do not prevent compromised passwords.
Allow all users to use sudo without passwords
Why it's wrong here
This increases security risk.
Common exam traps
CompTIA often tests the misconception that a strong password policy is sufficient to prevent unauthorized access, but the trap here is that password-based authentication is inherently vulnerable to credential reuse, phishing, and offline cracking, whereas key-based authentication provides cryptographic proof of identity that cannot be easily stolen or guessed.
Detailed technical explanation
SSH key-based authentication uses asymmetric cryptography (RSA, ECDSA, or Ed25519) where the private key never leaves the client, and the server verifies the client's identity by challenging it to sign a message with the private key. The server stores the public key in the user's `~/.ssh/authorized_keys` file, and the SSH daemon (sshd) must have `PasswordAuthentication no` and `PubkeyAuthentication yes` in `/etc/ssh/sshd_config`. In a real-world scenario, even if an attacker obtains the password hash from `/etc/shadow`, they cannot authenticate without the private key, provided key-based authentication is enforced and password authentication is disabled.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
What to study next
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FAQ
Security — This question tests Security — Read the scenario before looking for a memorised answer..
The correct answer is: Configure SSH to use key-based authentication only — Option A is correct because configuring SSH to use key-based authentication only eliminates the risk of password-based attacks, such as brute-force or credential theft. Since the compromised user account was accessed via SSH using a password, disabling password authentication and requiring a private key ensures that an attacker cannot log in even if they obtain the user's password hash. This aligns with the principle of least privilege and strong authentication, as SSH keys are cryptographically bound to the client and are not transmitted over the network.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This XK0-005 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 XK0-005 exam.
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