Why sudo /usr/bin/less Is Dangerous: Shell Escape to Root
This EX200 practice question tests your understanding of manage security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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
User jane may run the following commands on this host:
(ALL) NOPASSWD: /usr/bin/less
Refer to the exhibit. What is the primary security concern with this sudo configuration?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Exhibit
User jane may run the following commands on this host:
(ALL) NOPASSWD: /usr/bin/less
A
The NOPASSWD option eliminates the need for a password.
Why wrong: While NOPASSWD is a risk, the main concern is the command choice.
B
The entry uses (ALL) instead of (root), allowing jane to run as any user.
Why wrong: While that is true, the main risk is the command's ability to spawn a shell.
C
The less command allows executing shell commands via !, enabling privilege escalation.
This is a well-known sudo escape vector.
D
The command /usr/bin/less can be used to read any file.
Why wrong: Reading files is a valid use of less and not a direct privilege escalation.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The less command allows executing shell commands via !, enabling privilege escalation.
Option C is correct because the `less` command, when executed with sudo, allows the user to escape to a shell by typing `!command` from within the pager. This bypasses the intended restriction of only running `/usr/bin/less` as root, enabling arbitrary command execution with elevated privileges. The NOPASSWD directive further compounds the risk by removing the password prompt, making the escalation trivial.
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 NOPASSWD option eliminates the need for a password.
Why it's wrong here
While NOPASSWD is a risk, the main concern is the command choice.
✗
The entry uses (ALL) instead of (root), allowing jane to run as any user.
Why it's wrong here
While that is true, the main risk is the command's ability to spawn a shell.
✓
The less command allows executing shell commands via !, enabling privilege escalation.
Why this is correct
This is a well-known sudo escape vector.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The command /usr/bin/less can be used to read any file.
Why it's wrong here
Reading files is a valid use of less and not a direct privilege escalation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates focus on the NOPASSWD or the (ALL) syntax, missing the fact that the command itself (`less`) has built-in shell escape capabilities that can be exploited for privilege escalation.
Trap categories for this question
Command / output trap
While NOPASSWD is a risk, the main concern is the command choice.
Detailed technical explanation
How to think about this question
The `less` command, like `more` and `vim`, supports shell escapes via `!` when invoked with sudo, because the pager retains the elevated privileges. This is a classic example of a 'sudo pager escape' vulnerability, often listed in GTFOBins (GTFOBins.github.io). In a real-world scenario, an administrator might grant sudo access to `less` for log viewing, inadvertently allowing a user to run `sudo less /etc/shadow` and then `!bash` to gain a root shell.
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.
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.
Manage security — This question tests Manage security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The less command allows executing shell commands via !, enabling privilege escalation. — Option C is correct because the `less` command, when executed with sudo, allows the user to escape to a shell by typing `!command` from within the pager. This bypasses the intended restriction of only running `/usr/bin/less` as root, enabling arbitrary command execution with elevated privileges. The NOPASSWD directive further compounds the risk by removing the password prompt, making the escalation trivial.
What should I do if I get this EX200 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: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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