The answer is the principle of least privilege. This is correct because a default-deny ACL, which blocks all traffic unless explicitly permitted, directly enforces the core tenet of least privilege: granting only the minimum necessary access rights for a subject to perform its required function. By denying everything by default, the firewall ensures no implicit trust or unintended permissions exist, forcing every allowed action to be a deliberate, justified exception. On the CISSP exam, this concept tests your understanding of how access control mechanisms implement security principles; a common trap is confusing default-deny with need-to-know, but remember that least privilege focuses on the minimum rights for a role, while need-to-know restricts access to specific data. A strong memory tip is to think of a bouncer at a VIP event: they deny entry to everyone not on the explicit guest list, which is the very essence of least privilege in action.
CISSP Security and Risk Management Practice Question
This CISSP practice question tests your understanding of security and risk management. 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
Refer to the exhibit.
Syslog entry:
Mar 15 14:23:01 firewall: %SEC-6-IPACCESSLOGP: list 100 denied udp 10.0.0.5(1234) -> 192.168.1.1(53) 5 packets
Refer to the exhibit. A security analyst reviews this syslog entry from a firewall. The firewall's ACL is configured to deny all traffic by default except what is explicitly permitted. This is an example of which security principle?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Least privilege
The principle of least privilege grants only necessary access; default-deny (deny all by default) is an implementation of this principle.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Least privilege
Why this is correct
Least privilege ensures only necessary access is granted; default-deny enforces this.
Related concept
Authentication checks who the user is.
✗
Separation of duties
Why it's wrong here
Separation of duties divides tasks; not related to default-deny.
✗
Need to know
Why it's wrong here
Need to know is about data access based on job function, not network rules.
✗
Defense in depth
Why it's wrong here
Defense in depth uses multiple layers, not just default-deny.
Common exam traps
Common exam trap: authentication is not authorization
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Detailed technical explanation
How to think about this question
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
KKey Concepts to Remember
Authentication checks who the user is.
Authorization controls what the user is allowed to do after login.
Privilege levels affect access to EXEC and configuration commands.
AAA, TACACS+ and RADIUS can separate login success from command access.
TExam Day Tips
→Do not assume successful login means full administrative access.
→Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
→Separate login problems from permission problems before choosing the answer.
Key takeaway
Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Real-world example
How this comes up in practice
A security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related CISSP questions on access control and AAA configuration.
Security and Risk Management — This question tests Security and Risk Management — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: Least privilege — The principle of least privilege grants only necessary access; default-deny (deny all by default) is an implementation of this principle.
What should I do if I get this CISSP question wrong?
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related CISSP questions on access control and AAA configuration.
What is the key concept behind this question?
Authentication checks who the user is.
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Question Discussion
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