- A
User charlie can log in using a public key.
Why wrong: Charlie is not in AllowUsers, so access is denied.
- B
User bob can log in using a public key.
Correct. Password authentication is disabled, but public key is allowed, and bob is in AllowUsers.
- C
User alice can log in using a password.
Why wrong: PasswordAuthentication no disables all password logins.
- D
Root can log in using a valid password.
Why wrong: PermitRootLogin no disallows root login regardless of method.
Question 852 of 981
XK0-005 Security Practice Question
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.
An administrator configures /etc/ssh/sshd_config with the following settings: PermitRootLogin no, PasswordAuthentication no, AllowUsers alice bob, MaxAuthTries 2. After restarting sshd, which of the following is true?
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
✓
User bob can log in using a public key.
PasswordAuthentication no disables password logins, so public key authentication is required. PermitRootLogin no prevents root login entirely. AllowUsers restricts to alice and bob only. MaxAuthTries 2 limits authentication attempts. So root cannot log in even with keys, and alice/bob must use keys.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
User charlie can log in using a public key.
Why it's wrong here
Charlie is not in AllowUsers, so access is denied.
- ✓
User bob can log in using a public key.
Why this is correct
Correct. Password authentication is disabled, but public key is allowed, and bob is in AllowUsers.
Related concept
Standard ACLs match source addresses.
- ✗
User alice can log in using a password.
Why it's wrong here
PasswordAuthentication no disables all password logins.
- ✗
Root can log in using a valid password.
Why it's wrong here
PermitRootLogin no disallows root login regardless of method.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
- Standard ACLs match source addresses.
- Extended ACLs can match source, destination, protocol and ports.
- The first matching ACL entry is used.
- There is usually an implicit deny at the end.
TExam Day Tips
- Check inbound versus outbound direction.
- Read the ACL from top to bottom.
- Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related XK0-005 ACL questions on filtering logic and placement.
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FAQ
Questions learners often ask
What does this XK0-005 question test?
Security — This question tests Security — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: User bob can log in using a public key. — PasswordAuthentication no disables password logins, so public key authentication is required. PermitRootLogin no prevents root login entirely. AllowUsers restricts to alice and bob only. MaxAuthTries 2 limits authentication attempts. So root cannot log in even with keys, and alice/bob must use keys.
What should I do if I get this XK0-005 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related XK0-005 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Last reviewed: Jul 4, 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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