This XK0-005 practice question tests your understanding of security. Compare every option against the stated constraints before choosing — the best answer satisfies all requirements, not just the most obvious one. 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 Linux administrator discovers that a user's home directory contains a file with setuid bit set, owned by root. The file is not part of any authorized software. What is the most appropriate immediate action?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove the setuid bit with 'chmod u-s <file>'
Option D is correct because the immediate priority is to neutralize the unauthorized setuid root binary, which poses a privilege escalation risk. Removing the setuid bit with 'chmod u-s' disables the ability for any user to execute the file with root privileges, containing the threat without destroying evidence that may be needed for forensic analysis. This aligns with security best practices of preserving artifacts while mitigating active risks.
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.
✗
Move the file to /tmp for further analysis
Why it's wrong here
Moving does not remove the setuid bit; the risk remains.
✗
Delete the file immediately to remove the threat
Why it's wrong here
Deleting may destroy evidence needed for investigation.
✗
Change the file owner to the user with 'chown user:user <file>'
Why it's wrong here
Changing ownership does not remove the setuid bit; root ownership is required for setuid to be effective.
✓
Remove the setuid bit with 'chmod u-s <file>'
Why this is correct
This removes the setuid bit, preventing privilege escalation, while preserving the file.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose deletion (Option B) as the 'obvious' fix, overlooking the forensic value of the file and the fact that removing the setuid bit is a less destructive and equally effective containment measure.
Detailed technical explanation
How to think about this question
The setuid bit (mode 4xxx) on an executable file causes the process to run with the effective UID of the file owner, not the invoking user. When owned by root, this grants full superuser privileges to any user who executes it, making it a classic backdoor mechanism. In real-world incident response, removing the setuid bit is a containment step before deeper analysis (e.g., checking file hashes against known malware databases, reviewing audit logs for execution).
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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
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: Remove the setuid bit with 'chmod u-s <file>' — Option D is correct because the immediate priority is to neutralize the unauthorized setuid root binary, which poses a privilege escalation risk. Removing the setuid bit with 'chmod u-s' disables the ability for any user to execute the file with root privileges, containing the threat without destroying evidence that may be needed for forensic analysis. This aligns with security best practices of preserving artifacts while mitigating active risks.
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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