The answer is that the firewall is blocking Samba ports 137, 138, 139, and 445. This is correct because after a system update on Ubuntu 22.04, ufw rules can be reset to defaults, and the administrator’s `ufw status` output shows only SSH allowed—meaning Samba’s required NetBIOS and SMB ports are silently dropped. Since smbd and nmbd are running and AppArmor shows no denials, the firewall is the only remaining barrier. On the CompTIA Linux+ XK0-005 exam, this scenario tests your ability to distinguish between service, firewall, and MAC (AppArmor/SELinux) issues—a common trap is assuming AppArmor is the culprit when it’s actually a missing firewall rule. Remember that Samba needs both NetBIOS (UDP 137-138, TCP 139) and direct SMB (TCP 445) open. Memory tip: “Samba’s four friends: 137, 138, 139, and 445—if ufw blocks them, your shares won’t arrive.”
XK0-005 Security Practice Question
This XK0-005 practice question tests your understanding of security. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 company uses a Linux server running Ubuntu 22.04 LTS as a file server to share documents via Samba. The server has been in operation for over a year without issues. Following a routine system update that included kernel patches and updated Samba packages, users began reporting that they could no longer access any shared folders. The administrator verifies that the smbd and nmbd services are running and have not failed. The Samba configuration has not been changed recently. The server uses ufw as its firewall. When the administrator runs 'ufw status', the output shows that only SSH (port 22) is allowed. The administrator checks for SELinux but finds it is not installed; however, AppArmor is active and the smbd profile is in enforce mode. The administrator examines the AppArmor logs and finds no denials related to smbd. Which of the following is the most likely reason for the connectivity failure?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The firewall is blocking Samba ports 137, 138, 139, and 445.
The firewall (ufw) is only allowing SSH (port 22), which means Samba ports 137/138 (NetBIOS), 139 (SMB over NetBIOS), and 445 (SMB over TCP) are blocked. Since the smbd and nmbd services are running and AppArmor shows no denials, the most likely cause is that the firewall rules were reset or not updated after the system update, preventing Samba traffic from reaching the server.
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.
✓
The firewall is blocking Samba ports 137, 138, 139, and 445.
Why this is correct
ufw only allows SSH; Samba ports are not permitted.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The Samba configuration file was corrupted during the update.
Why it's wrong here
Unlikely; configuration not changed and service starts without errors.
✗
The kernel update changed the default file system mount options, restricting access.
Why it's wrong here
No evidence of mount issues; users cannot even connect to shares.
✗
The AppArmor profile is preventing smbd from binding to network interfaces.
Why it's wrong here
AppArmor logs show no denials, suggesting no such restriction.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may focus on AppArmor or SELinux because they are security modules, but the absence of denials in AppArmor logs and the explicit ufw output showing only SSH allowed points directly to the firewall as the culprit.
Trap categories for this question
Command / output trap
AppArmor logs show no denials, suggesting no such restriction.
Detailed technical explanation
How to think about this question
Samba relies on ports 137 (NetBIOS name service), 138 (NetBIOS datagram), 139 (NetBIOS session), and 445 (SMB over TCP). Ufw is a frontend for iptables, and after a system update, firewall rules may be lost if the ufw configuration was not saved or if the update reset the default policy to deny. The fact that only SSH is allowed suggests the firewall was reconfigured or the default deny policy was applied, blocking all Samba ports.
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 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this XK0-005 question in full detail.
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The firewall is blocking Samba ports 137, 138, 139, and 445. — The firewall (ufw) is only allowing SSH (port 22), which means Samba ports 137/138 (NetBIOS), 139 (SMB over NetBIOS), and 445 (SMB over TCP) are blocked. Since the smbd and nmbd services are running and AppArmor shows no denials, the most likely cause is that the firewall rules were reset or not updated after the system update, preventing Samba traffic from reaching the server.
What should I do if I get this XK0-005 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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