mediumMultiple Choice
CKS Practice Question: Auditing RBAC and find a ClusterRoleBinding named…
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?
⚠ Common exam trap
The trap here is that candidates may focus on the binding type (ClusterRoleBinding vs RoleBinding) or namespace usage, rather than recognizing that the core issue is the excessive privileges of the 'cluster-admin' role itself, regardless of how it is bound.
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
✓
It grants too broad permissions to the service account
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.
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 binding should be a RoleBinding instead of ClusterRoleBinding
Why it's wrong here
A RoleBinding cannot grant cluster-admin's cluster-scoped permissions; it only binds within one namespace, so converting it would actually reduce privilege. The genuine concern is that cluster-admin is bound at all, giving full cluster control to a default-namespace service account.
- ✓
It grants too broad permissions to the service account
Why this is correct
The cluster-admin ClusterRole carries wildcard verbs and resources across every namespace. Binding it to a default-namespace service account means any pod using that account can read secrets, escalate privileges and modify workloads cluster-wide, far exceeding what the workload requires.
- ✗
The service account name must be changed
Why it's wrong here
Renaming the service account changes nothing about the permissions granted; the ClusterRoleBinding still confers cluster-admin cluster-wide. The concern is the excessive privilege and the binding's cluster scope, not the identity's name. Renaming would only matter for hygiene or audit labelling, never for reducing access.
- ✗
The binding is fine as long as the service account is used in the default namespace
Why it's wrong here
Namespace scoping does not contain a ClusterRoleBinding: cluster-admin grants full control over every namespace and cluster-scoped resource, so compromise of that service account is cluster-wide regardless of where it runs. Treating namespace placement as a containment boundary is the tempting error.
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 |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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