- A
The risk is only if the service account is used by external users
Why wrong: Pods in the cluster can use the service account.
- B
The ClusterRoleBinding is invalid because it uses a namespace-scoped service account
Why wrong: Service accounts are namespaced but can be used in ClusterRoleBindings.
- C
Any pod using the default service account in kube-system has cluster-admin privileges
The service account inherits the cluster-admin role.
- D
No risk, as it is limited to kube-system namespace
Why wrong: ClusterRoleBindings are cluster-wide, not limited to a namespace.
Question 992 of 997
Why Binding Cluster-Admin to a Service Account Violates Least Privilege
This CKS practice question tests your understanding of cluster setup and hardening. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
You are auditing RBAC and find a ClusterRoleBinding named 'admin-binding' that binds the 'cluster-admin' ClusterRole to the service account 'default' in namespace 'kube-system'. What is the risk?
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
✓
Any pod using the default service account in kube-system has cluster-admin privileges
Option C is correct because the ClusterRoleBinding 'admin-binding' binds the 'cluster-admin' ClusterRole to the 'default' service account in the 'kube-system' namespace. Since ClusterRoleBindings are cluster-scoped, they grant permissions across all namespaces. Any pod in the 'kube-system' namespace that uses the 'default' service account (which is the default if no other service account is specified) will inherit cluster-admin privileges, allowing full control over the entire cluster.
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 risk is only if the service account is used by external users
Why it's wrong here
Pods in the cluster can use the service account.
- ✗
The ClusterRoleBinding is invalid because it uses a namespace-scoped service account
Why it's wrong here
Service accounts are namespaced but can be used in ClusterRoleBindings.
- ✓
Any pod using the default service account in kube-system has cluster-admin privileges
Why this is correct
The service account inherits the cluster-admin role.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
No risk, as it is limited to kube-system namespace
Why it's wrong here
ClusterRoleBindings are cluster-wide, not limited to a namespace.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CNCF often tests the distinction between RoleBindings (namespace-scoped) and ClusterRoleBindings (cluster-scoped), and the trap here is that candidates mistakenly think a ClusterRoleBinding to a namespace-scoped service account is invalid or limited to that namespace.
Detailed technical explanation
How to think about this question
Under the hood, a ClusterRoleBinding binds a ClusterRole (which contains non-namespaced resources like nodes and persistent volumes) to subjects, and the binding itself is not namespaced. The 'default' service account in any namespace is automatically mounted into pods unless overridden, so a pod in kube-system using the default service account will have a token that authenticates with the cluster-admin privileges. In a real-world scenario, a compromised pod in kube-system (e.g., a vulnerable kube-proxy or coredns) could leverage this to escalate privileges and control the entire cluster.
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.
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 |
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.
- →
Cluster Setup and Hardening — study guide chapter
Learn the concepts, then practise the questions
- →
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FAQ
Questions learners often ask
What does this CKS question test?
Cluster Setup and Hardening — This question tests Cluster Setup and Hardening — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Any pod using the default service account in kube-system has cluster-admin privileges — Option C is correct because the ClusterRoleBinding 'admin-binding' binds the 'cluster-admin' ClusterRole to the 'default' service account in the 'kube-system' namespace. Since ClusterRoleBindings are cluster-scoped, they grant permissions across all namespaces. Any pod in the 'kube-system' namespace that uses the 'default' service account (which is the default if no other service account is specified) will inherit cluster-admin privileges, allowing full control over the entire cluster.
What should I do if I get this CKS 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
4 more ways this is tested on CKS
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A ClusterRoleBinding named 'admin-binding' binds the cluster-admin ClusterRole to a service account 'sa-admin' in namespace 'ns1'. What is the security concern?
hard- ✓ A.The service account 'sa-admin' can access resources in all namespaces
- B.ClusterRoleBinding should be replaced by RoleBinding for cluster-scoped resources
- C.The service account token is automatically mounted
- D.ClusterRoleBinding should not be used for service accounts
Why A: A ClusterRoleBinding grants permissions cluster-wide, meaning the service account 'sa-admin' in namespace 'ns1' can access resources in all namespaces, not just its own. This violates the principle of least privilege by providing excessive access beyond the intended scope.
Variation 2. An administrator runs 'kubectl get clusterrolebindings' and notices a ClusterRoleBinding named 'admin-binding' that binds the 'cluster-admin' ClusterRole to a service account in the 'default' namespace. What security concern does this raise?
medium- ✓ A.The service account can now perform any action across all namespaces, which violates least-privilege.
- B.The service account can only access resources in the 'default' namespace.
- C.No concern; service accounts are allowed to have cluster-admin.
- D.The ClusterRoleBinding should be replaced with a RoleBinding.
Why A: A ClusterRoleBinding grants cluster-wide permissions, and the 'cluster-admin' ClusterRole provides superuser access to perform any action on any resource across all namespaces. Binding this to a service account violates the principle of least privilege because the service account gains unrestricted access to the entire cluster, including sensitive system resources, rather than being limited to only the permissions necessary for its function.
Variation 3. You are auditing RBAC and find a ClusterRoleBinding named 'admin-binding' that binds the 'cluster-admin' ClusterRole to a service account in the 'default' namespace. What is the security concern?
medium- A.The binding should be a RoleBinding instead of ClusterRoleBinding
- ✓ B.It grants too broad permissions to the service account
- C.The service account name must be changed
- D.The binding is fine as long as the service account is used in the default namespace
Why B: The 'cluster-admin' ClusterRole grants super-user permissions across the entire cluster, including access to all namespaces and all resources. Binding this role to a service account via a ClusterRoleBinding gives that service account unrestricted cluster-wide privileges, which violates the principle of least privilege. This is a significant security concern because if the service account is compromised, an attacker gains full control over the cluster.
Variation 4. A developer created a ClusterRoleBinding that grants cluster-admin to a service account. What is the security concern?
medium- A.Service accounts must use RoleBindings only
- B.ClusterRoleBindings are deprecated
- C.Service accounts cannot use ClusterRoleBindings
- ✓ D.It gives the service account full cluster-wide permissions, which is excessive
Why D: Option D is correct because granting a service account cluster-admin via a ClusterRoleBinding provides unrestricted, cluster-wide permissions, violating the principle of least privilege. This is a significant security risk as it allows the service account to perform any action on any resource in any namespace, including modifying RBAC rules, secrets, or node configurations. In Kubernetes, service accounts should be bound only to the minimal roles required for their function, typically using RoleBindings scoped to a specific namespace.
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Last reviewed: Jun 30, 2026
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