The answer is disabling unnecessary services, along with enforcing strong password policies and removing unused software packages. Disabling unnecessary services directly reduces the Linux attack surface by closing network ports, stopping background daemons, and eliminating code paths that an attacker could exploit. Each running service is a potential entry point, so stopping and masking services not required for the server’s role—using systemctl disable and mask—minimizes exploitable components. On the CompTIA Linux+ XK0-005 exam, this concept tests your understanding of system hardening principles, often appearing in scenario-based questions where you must identify which actions shrink the attack surface versus those that merely improve logging or performance. A common trap is confusing service disabling with simply stopping a service temporarily; remember that masking prevents re-enablement. For a quick memory tip, think “D.U.M.P.”—Disable, Uninstall, Mask, and Patch—to recall the core actions that shrink the attack surface.
XK0-005 Security Practice Question
This XK0-005 practice question tests your understanding of security. 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.
An administrator is hardening a Linux server. Which three of the following actions reduce the attack surface? (Select THREE).
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Disabling unnecessary services
Disabling unnecessary services reduces the attack surface by eliminating potential entry points for attackers. Each running service exposes network ports, system resources, and code paths that could contain vulnerabilities. By stopping and masking services not required for the server's role (e.g., using systemctl disable and mask), the administrator minimizes the number of exploitable components.
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.
✗
Setting default umask to 022
Why it's wrong here
This is a default setting and does not reduce attack surface significantly; a more restrictive umask like 077 would.
✓
Disabling unnecessary services
Why this is correct
Reduces potential entry points for attackers.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enabling USB mass storage kernel module
Why it's wrong here
This increases attack surface by allowing USB storage devices.
✓
Using a host-based firewall
Why this is correct
Controls network traffic and blocks unwanted connections.
Related concept
Read the scenario before looking for a memorised answer.
✓
Enforcing strong password policies
Why this is correct
Mitigates brute-force and guessing attacks.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the misconception that setting a restrictive umask or enabling USB storage is a hardening action, when in fact umask 022 is the default and permissive, and enabling USB storage expands the attack surface rather than reducing it.
Detailed technical explanation
How to think about this question
The attack surface concept in Linux hardening is often quantified by the number of listening ports (netstat -tuln), running daemons (systemctl list-units --type=service), and loaded kernel modules (lsmod). Disabling services like CUPS, Avahi, or Bluetooth on a web server reduces the chance of exploiting vulnerabilities such as CVE-2021-3560 in polkit or buffer overflows in unused network stacks. A host-based firewall (e.g., iptables or nftables) further restricts traffic to only necessary ports, complementing service disabling.
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: Disabling unnecessary services — Disabling unnecessary services reduces the attack surface by eliminating potential entry points for attackers. Each running service exposes network ports, system resources, and code paths that could contain vulnerabilities. By stopping and masking services not required for the server's role (e.g., using systemctl disable and mask), the administrator minimizes the number of exploitable components.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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