This LFCS practice question tests your understanding of essential commands. 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 security audit reveals that a sensitive file '/etc/shadow' has been modified. The file's permissions are set to 600 and owned by root. However, the audit logs show that a service account 'webapp' was able to read the file. The 'webapp' user is not in the root group. Which of the following is the most likely method the 'webapp' user used to read the file?
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 file has an Access Control List (ACL) granting read permission to 'webapp'.
Option C is correct because an Access Control List (ACL) can grant specific permissions to a user or group beyond the traditional Unix permission model. Even though the file's mode is 600 (owner read/write only) and owned by root, a setfacl command could have added an ACL entry (e.g., 'u:webapp:r') that explicitly allows the 'webapp' user to read /etc/shadow. This is a common method to give a service account access to a sensitive file without changing its ownership or group membership.
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 file is a hard link to another file that is readable by 'webapp'.
Why it's wrong here
Hard links share the same inode and permissions; if the original is 600, the link is also 600.
✗
The 'webapp' user exploited a SUID binary that reads the file.
Why it's wrong here
Exploiting a SUID binary is possible but more complex and less common.
✓
The file has an Access Control List (ACL) granting read permission to 'webapp'.
Why this is correct
ACLs override base permissions and can grant access to specific users.
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 'webapp' user used 'sudo' to read the file as root.
Why it's wrong here
Sudo usage would appear in logs and require configuration; less likely without evidence.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume traditional Unix permissions (owner/group/other) are the only way to control access, overlooking that ACLs can grant specific users read permission even when the file's mode appears restrictive (e.g., 600).
Detailed technical explanation
How to think about this question
ACLs in Linux are implemented via extended attributes (xattrs) and managed with getfacl/setfacl commands. The 'getfacl /etc/shadow' command would reveal any ACL entries, such as 'user:webapp:r--', which override the traditional mode bits for that specific user. In real-world scenarios, service accounts like 'webapp' are often granted minimal access via ACLs to avoid changing ownership or group membership, which could break other security policies.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Essential Commands — This question tests Essential Commands — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The file has an Access Control List (ACL) granting read permission to 'webapp'. — Option C is correct because an Access Control List (ACL) can grant specific permissions to a user or group beyond the traditional Unix permission model. Even though the file's mode is 600 (owner read/write only) and owned by root, a setfacl command could have added an ACL entry (e.g., 'u:webapp:r') that explicitly allows the 'webapp' user to read /etc/shadow. This is a common method to give a service account access to a sensitive file without changing its ownership or group membership.
What should I do if I get this LFCS 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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Question Discussion
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