CAS-004 Security Engineering Practice Question
A security engineer is designing a system that must enforce mandatory access control (MAC) based on security labels. The system must ensure that users cannot read data above their clearance level and cannot write data to lower classification levels. Which security model BEST fits these requirements?
⚠ Common exam trap
The trap here is mixing up confidentiality and integrity models, especially Bell-LaPadula and Biba, which have opposite rules.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Bell-LaPadula model
The requirements describe the classic confidentiality model: prevent reading above clearance (no-read-up) and prevent writing to lower levels (no-write-down). The Bell-LaPadula model explicitly defines these properties. Biba is for integrity, Clark-Wilson for integrity transactions, and Brewer-Nash for conflict of interest. Thus, Bell-LaPadula is the correct choice.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Bell-LaPadula model
Why this is correct
The Bell-LaPadula model enforces confidentiality through the no-read-up and no-write-down properties. The no-read-up rule prevents subjects from reading objects at a higher classification, and the no-write-down rule prevents writing to lower classifications. This directly matches the requirement to restrict reading above clearance and writing to lower levels.
- ✗
Clark-Wilson model
Why it's wrong here
The Clark-Wilson model enforces integrity through well-formed transactions and separation of duties. It does not use security labels or clearance levels for mandatory access control. While it provides strong integrity controls, it does not address the confidentiality requirements of reading above clearance or writing down.
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Brewer-Nash model
Why it's wrong here
The Brewer-Nash model, also known as the Chinese Wall model, prevents conflicts of interest by dynamically restricting access based on a user's previous accesses. It does not enforce static clearance levels or the no-read-up/no-write-down rules. Therefore, it is not suitable for the described mandatory access control requirements.
- ✗
Biba model
Why it's wrong here
The Biba model focuses on integrity, with no-read-down and no-write-up properties. It prevents reading lower integrity data and writing to higher integrity levels. This is the opposite of the stated requirements, which are about confidentiality and preventing write-down. Therefore, Biba does not fit the scenario.
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
Go deeper
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
This CAS-005 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CAS-005 exam.