The correct answer is that the SUID bit is set, allowing users to run passwd with root privileges to change their own password. This security implication stems from the Set User ID (SUID) permission, which appears as an 's' in the owner's execute position of the file's mode (e.g., -rwsr-xr-x). When the SUID bit is set on /usr/bin/passwd, any user executing it temporarily gains the effective UID of the file owner (root), enabling the command to write to /etc/shadow—a file normally restricted to root—while strictly limiting changes to the invoking user's own password. On the CompTIA Linux+ XK0-005 exam, this scenario tests your understanding of how SUID elevates privileges for specific, trusted binaries, and a common trap is mistaking this standard mechanism for a vulnerability. Remember: the 's' in the owner's execute spot means "switch user ID" for that command only. A useful memory tip is "SUID: Small UID switch, big privilege lift—but only for the task at hand."
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.
Exhibit
Refer to the exhibit.
ls -la /usr/bin/passwd
-rwsr-xr-x 1 root root 68208 Apr 1 2024 /usr/bin/passwd
Based on the exhibit, what best describes the security implication?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The SUID bit is set, allowing users to run passwd with root privileges to change their own password.
The SUID (Set User ID) bit is set on the /usr/bin/passwd file, as indicated by the 's' in the owner's execute position (e.g., -rwsr-xr-x). This allows any user to run the passwd command with the effective UID of the file owner (root), enabling them to change their own password by writing to /etc/shadow, which is otherwise only writable by root. This is a standard security mechanism, not a vulnerability, as the passwd binary is carefully designed to only allow password changes for the invoking user.
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 SUID bit is set, allowing users to run passwd with root privileges to change their own password.
Why this is correct
The 's' in the user execute position indicates SUID.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The file is world-writable.
Why it's wrong here
World permissions are 'r-x' (read and execute), not writable.
✗
The SGID bit is set, allowing users to run passwd with group root.
Why it's wrong here
SGID would show 's' in the group execute position, which is not the case here ('x' in group).
✗
The sticky bit is set, preventing deletion of the file.
Why it's wrong here
Sticky bit would show 't' at the end of the permissions, not present.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between SUID, SGID, and sticky bits by presenting a file listing with an 's' in the owner's execute position and expecting candidates to recognize it as SUID, not confusing it with SGID (which would be in the group position) or the sticky bit (which would be a 't' in the others position).
Trap categories for this question
Command / output trap
SGID would show 's' in the group execute position, which is not the case here ('x' in group).
Detailed technical explanation
How to think about this question
The SUID bit works by changing the effective UID of the process to the file owner's UID (0 for root) during execution, as defined in the POSIX standard. The passwd binary is a classic example of a 'setuid root' program; it must be carefully audited to prevent privilege escalation, such as through buffer overflows or improper input validation. In modern Linux systems, capabilities (e.g., CAP_CHOWN, CAP_FOWNER) are sometimes used instead of full SUID root to reduce security risks, but the traditional SUID bit remains common for passwd.
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: The SUID bit is set, allowing users to run passwd with root privileges to change their own password. — The SUID (Set User ID) bit is set on the /usr/bin/passwd file, as indicated by the 's' in the owner's execute position (e.g., -rwsr-xr-x). This allows any user to run the passwd command with the effective UID of the file owner (root), enabling them to change their own password by writing to /etc/shadow, which is otherwise only writable by root. This is a standard security mechanism, not a vulnerability, as the passwd binary is carefully designed to only allow password changes for the invoking user.
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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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