The answer is the Bell-LaPadula model, which enforces mandatory access control through the 'no read up, no write down' principle. This rule directly maps to the exhibit’s policy: a subject at a given security level cannot read objects at a higher level (Simple Security Property) and cannot write to objects at a lower level (Star Property), ensuring that information never flows from a higher classification to a lower one. On the CISSP exam, this model is the definitive choice for any scenario focused on confidentiality, often appearing alongside the Biba model (which addresses integrity with opposite rules). A common trap is confusing the two—remember that Bell-LaPadula cares about keeping secrets, so it blocks reading up and writing down. For a quick memory tip, think “BLP = Bell LaPadula = Big Lock on Papers,” emphasizing its role in preventing unauthorized disclosure of classified data.
CISSP Security Architecture and Engineering Practice Question
This CISSP practice question tests your understanding of security architecture and engineering. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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
The TSF shall enforce the Access Control SFP on all subjects and objects covered by the following rules:
(a) Subjects with a security level less than the object's security level are denied read access.
(b) Subjects with a security level greater than the object's security level are denied write access.
Refer to the exhibit. Which security model does this policy enforce?
The TSF shall enforce the Access Control SFP on all subjects and objects covered by the following rules:
(a) Subjects with a security level less than the object's security level are denied read access.
(b) Subjects with a security level greater than the object's security level are denied write access.
A
Biba
Why wrong: Biba enforces no read down and no write up.
B
Brewer-Nash
Why wrong: Brewer-Nash prevents conflict of interest, not the stated rules.
C
Bell-LaPadula
Correct. BLP enforces no read up and no write down.
D
Clark-Wilson
Why wrong: Clark-Wilson focuses on integrity through transformation procedures and constrained data items.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Bell-LaPadula
The Bell-LaPadula model enforces a mandatory access control policy based on the 'no read up, no write down' principle, which directly corresponds to the exhibit's rule that a subject at a given security level cannot read objects at a higher level (Simple Security Property) and cannot write to objects at a lower level (Star Property). This is the only model among the options that specifically addresses confidentiality through hierarchical classification levels and the prevention of information flow from higher to lower security levels.
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.
✗
Biba
Why it's wrong here
Biba enforces no read down and no write up.
✗
Brewer-Nash
Why it's wrong here
Brewer-Nash prevents conflict of interest, not the stated rules.
✓
Bell-LaPadula
Why this is correct
Correct. BLP enforces no read up and no write down.
Related concept
Read the scenario before looking for a memorised answer.
✗
Clark-Wilson
Why it's wrong here
Clark-Wilson focuses on integrity through transformation procedures and constrained data items.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the confusion between Bell-LaPadula (confidentiality, no read up/no write down) and Biba (integrity, no read down/no write up), so candidates mistakenly pick Biba when they see a policy about preventing information flow from high to low, not realizing the direction of the rules is reversed.
Detailed technical explanation
How to think about this question
Under the hood, Bell-LaPadula uses a lattice of security levels (e.g., Unclassified, Confidential, Secret, Top Secret) and categories (compartments) to define the subject's clearance and object's classification. The Simple Security Property (ss-property) ensures a subject cannot read an object with a higher classification, while the Star Property (*-property) prevents a subject from writing to an object with a lower classification, thus preventing a Trojan horse from leaking classified data downward. In real-world scenarios, this model is commonly implemented in military and government systems where confidentiality is paramount, such as in multilevel secure (MLS) operating systems like SELinux with strict MLS 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 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. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. 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.
Security Architecture and Engineering — This question tests Security Architecture and Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Bell-LaPadula — The Bell-LaPadula model enforces a mandatory access control policy based on the 'no read up, no write down' principle, which directly corresponds to the exhibit's rule that a subject at a given security level cannot read objects at a higher level (Simple Security Property) and cannot write to objects at a lower level (Star Property). This is the only model among the options that specifically addresses confidentiality through hierarchical classification levels and the prevention of information flow from higher to lower security levels.
What should I do if I get this CISSP 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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