hardMultiple ChoiceObjective-mapped
CISSP Practice Question: Is reviewing the architecture of a system that…
A security engineer is reviewing the architecture of a system that uses the Bell-LaPadula model. The system has subjects with security clearances and objects with classifications. To prevent covert timing channels, which additional control should be implemented?
⚠ Common exam trap
Many exam-takers confuse covert timing channels with covert storage channels (which involve writing data to a shared attribute) and incorrectly choose audit logging or encryption as a catch-all solution, rather than recognizing that timing channels require controlling the concurrency of resource access.
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
✓
Disable concurrent access to shared resources
Covert timing channels exploit the ability of a subject to modulate the timing of its access to a shared resource, thereby leaking information to another subject at a different security level. The Bell-LaPadula model enforces mandatory access control (MAC) but does not inherently prevent these channels. Disabling concurrent access to shared resources (option C) eliminates the ability to use timing variations as a signaling mechanism, directly addressing the covert channel at the resource scheduling level.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enforce strict data labeling
Why it's wrong here
Enforcing strict data labeling, often associated with mandatory access control models like Bell-LaPadula, primarily focuses on preventing unauthorized direct access to information based on security classifications. While crucial for confidentiality, this mechanism does not inherently mitigate covert timing channels. These channels exploit observable differences in system response times or resource consumption, which are not directly controlled or prevented by data labels themselves, allowing information to be inferred indirectly.
- ✗
Implement audit logging
Why it's wrong here
Implementing comprehensive audit logging is a critical security control for detection and forensic analysis, recording system events and user actions. However, audit logs primarily serve to identify suspicious activities after they have occurred or to provide evidence for post-incident investigation. Covert timing channels, by their nature, exploit subtle variations in system behavior rather than direct access violations, making them extremely difficult to prevent solely through logging mechanisms, though logs might sometimes reveal patterns indicative of their presence.
- ✓
Disable concurrent access to shared resources
Why this is correct
Disabling or severely limiting concurrent access to shared system resources is a highly effective mitigation strategy against covert timing channels. These channels fundamentally rely on two or more processes interacting with a shared resource, where one process modulates the resource's state and another observes the resulting timing variations to infer information. By eliminating or restricting concurrency, the opportunity for one process to influence the timing observable by another through a shared medium is significantly reduced, thereby closing a primary avenue for such covert communication.
- ✗
Use encryption for data at rest
Why it's wrong here
Employing encryption for data at rest is a fundamental security measure designed to protect the confidentiality and integrity of stored information, rendering it unreadable to unauthorized entities. While essential for data protection, encryption primarily secures the content of the data itself. Covert timing channels, however, do not typically involve direct access to or decryption of sensitive data; instead, they exploit observable differences in system processing times or resource availability, which are unaffected by whether the underlying data is encrypted or not.
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
Related to this question
Learn chapter
Security Governance and Principles
Key term
Access control
Access control is the security practice of determining who or what is allowed to view, use, or enter a resource, and under what conditions.
Key term
Bell-LaPadula
A formal security model that prevents users from reading information at a higher classification level than their own and from writing information down to a lower classification level.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CISSP practice question is part of Courseiva's free ISC2 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 CISSP exam.