The answer is that a world-readable /etc/passwd file primarily allows attackers to enumerate valid system usernames and their UID mappings. This is a critical security issue because usernames are stored in the first colon-delimited field of each line, making them trivially extractable for password guessing or brute-force attacks. On the CompTIA Linux+ XK0-005 exam, this concept tests your understanding of file permission risks and user enumeration techniques; a common trap is confusing /etc/passwd with /etc/shadow, which stores hashed passwords and should never be world-readable. Remember that /etc/passwd is a user database, not a password database—think of it as a public phonebook that lists names (usernames) but not keys (passwords). A useful memory tip: "Passwd shows the door, Shadow holds the key."
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.
A security audit identifies that the system's /etc/passwd file is world-readable. Which three security issues does this pose? (Select THREE.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Attackers can obtain usernames easily.
Option B is correct because the /etc/passwd file contains a list of all system usernames. Since the file is world-readable, any user or attacker can easily read this file to enumerate valid usernames, which is a common first step in password guessing or brute-force attacks. Usernames are stored in the first colon-delimited field of each line, making them trivially extractable.
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.
✗
Attackers can read the encrypted passwords.
Why it's wrong here
Historically passwords were stored in /etc/passwd, but modern systems store them in /etc/shadow.
✓
Attackers can obtain usernames easily.
Why this is correct
/etc/passwd lists all local usernames.
Related concept
Read the scenario before looking for a memorised answer.
✓
Attackers can see home directory paths.
Why this is correct
Home directory paths are listed in /etc/passwd.
Related concept
Read the scenario before looking for a memorised answer.
✓
Attackers can see user ID mappings.
Why this is correct
The file contains UID and GID numbers for each user.
Related concept
Read the scenario before looking for a memorised answer.
✗
Attackers can read password hashes.
Why it's wrong here
Password hashes are stored in /etc/shadow, which is not world-readable.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the legacy practice of storing password hashes in /etc/passwd with the modern shadow password suite, and mistakenly select options A or E, not realizing that /etc/shadow is the actual hash store.
Detailed technical explanation
How to think about this question
The /etc/passwd file has seven colon-separated fields: username, password placeholder (x), UID, GID, GECOS, home directory, and shell. While the home directory path (field 6) and UID (field 3) are visible and can aid an attacker in targeting user-specific resources or identifying privileged accounts (UID 0), the password hash is never present in this file. In real-world scenarios, an attacker who gains local access can run 'cat /etc/passwd' to map out user accounts and their home directories, then use that information to craft targeted attacks.
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: Attackers can obtain usernames easily. — Option B is correct because the /etc/passwd file contains a list of all system usernames. Since the file is world-readable, any user or attacker can easily read this file to enumerate valid usernames, which is a common first step in password guessing or brute-force attacks. Usernames are stored in the first colon-delimited field of each line, making them trivially extractable.
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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