Role based access control (RBAC) is a native feature in Kubernetes integrated directly into the Kubernetes API. Cluster administrators use Kubernetes RBAC to enable fine grained management of user privileges within a Kubernetes cluster. With Kubernetes RBAC, administrators can regulate access to the Kubernetes API and Kubernetes cluster resources based on the roles assigned to users, groups, and service accounts.
Kubernetes role-based access control (RBAC) is a method for regulating access to computer or network resources based on the roles of individual users within an organization. In Kubernetes, RBAC enforces granular permission policies, determining who can access which resources and what operations they can perform. It maps users to roles, and roles to sets of permissions.
Kubernetes RBAC is critical for maintaining the security and integrity of a cluster. By implementing RBAC, organizations ensure that only authorized individuals have access to sensitive operations, reducing the risk of accidental or malicious alterations to the cluster’s state. It also helps comply with the principle of least privilege, providing only the access necessary for users to perform their jobs.
RBAC plays a central role in Kubernetes security, as it provides a framework for managing user permissions within a Kubernetes cluster. Effectively implementing Kubernetes RBAC rules prevents unauthorized users from performing sensitive operations that could compromise the cluster's security, such as deploying applications, accessing data, or modifying the cluster level configuration.
Cluster admins can build access control rules by defining specific default roles with associated permissions and binding these roles to users or service accounts. RBAC policies can be defined according to the needs and responsibilities of different users and applications within the Kubernetes cluster.
Let’s look at several areas that highlight the importance of Kubernetes RBAC for securely managing permissions.
Kubernetes RBAC enforces the principle of least privilege to ensure that human users, services, applications, and connected devices have the minimum permissions needed to perform their duties. Enforcing the principle of least privilege minimizes potential damage from accidental or malicious actions, limiting cluster exposure.
By automating access control decisions based on predefined roles, Kubernetes RBAC reduces the administrative overhead associated with managing user permissions.
Kubernetes RBAC allows for detailed and specific access control policies. Administrators can define fine-grained RBAC roles with permissions tailored to different users' or services' needs and manage complex permission structures across diverse teams and applications.
By restricting access to cluster resources and reducing the attack surface, Kubernetes RBAC prevents unauthorized access and privilege escalation cluster wide.
As Kubernetes environments grow, RBAC scales to manage access across an increasing number of users, applications, and resources. It provides the flexibility needed to adapt permissions quickly as RBAC roles change within an organization securely.
Within teams, Kubernetes RBAC supports the separation of duties and limits access only to the resources necessary for specific roles. This separation helps prevent conflicts of interest and reduces the risk of unauthorized changes or data breaches.
Kubernetes RBAC facilitates compliance with internal and external security policies and regulations by strictly managing who has access to what. It also simplifies auditing by monitoring and recording access. This makes it easier to verify that security policies are correctly enforced and provide related reports for audits.
RBAC roles and permissions in Kubernetes can be divided into two types — Role and ClusterRole.
In Kubernetes RBAC, Role defines permissions and grants access to resources such as pods, services, Secrets, and deployments. Kubernetes RBAC policies can be applied at the namespace level using Roles to allow a cluster admin to assign permissions (e.g., reading, writing, creating, or deleting) specific to resources within a namespace. Broad categories of roles include:
Unlike Roles, which are limited to a specific namespace, ClusterRoles allow cluster admins to grant permissions across the entire cluster. ClusterRoles are used to assign permissions that are applicable cluster wide, such as permissions for activities that span multiple namespaces or for resources that are not namespace specific (e.g., nodes).
Both Roles and ClusterRoles can be bound to users, groups, or service accounts using RoleBindings and ClusterRoleBindings.
RoleBindings are used to grant the permissions defined in a Role to a user, group, or service account within a specific namespace.
ClusterRoleBindings grant the permissions defined in a ClusterRole across the entire cluster. This means that if a ClusterRole is bound to a user, group, or service account using a ClusterRoleBinding, they will have the permissions defined in that ClusterRole in all namespaces. ClusterRoleBinding allows admins to grant cluster wide (non namespaced) permissions to specific users.
In Kubernetes RBAC, the roleRef field is a critical component of RoleBinding and ClusterRoleBinding objects. It specifies the role that the binding grants permissions to the subjects (e.g., users, groups, or service accounts) listed in the binding. This defines what actions the subjects can perform and on which resources, based on the permissions defined in the referred role.
With Kubernetes RBAC, permissions are defined by combining verbs. Permissions in Kubernetes RBAC are granular, and administrators can combine these verbs with resources and resource names to define specific types based on their intended use and scope. The following examples of verbs used to define permissions securely in Kubernetes RBAC are based on the actions they allow:
In Kubernetes, RBAC resources are defined using the apiVersion (e.g., v1 kind). Within the apiVersion, RBAC resources that can be defined to manage access control in a Kubernetes cluster are Role, ClusterRole, RoleBindings, and ClusterRoleBindings.
In Kubernetes, RBAC policies are configured using roles and role bindings. When defining an RBAC Role or ClusterRole, the Role metadata and ClusterRole metadata fields (e.g., namespace: default, name: pod reader) are crucial as they provide information about the role, including its name, namespace, labels, and annotations.
Custom roles can be created to tailor access permissions to specific needs beyond the default roles provided by Kubernetes. These roles can be created using Role or ClusterRole objects and specifying the verbs allowed on resources. Custom roles allow administrators to define specific permissions tailored to the needs of their users or applications.
Cross-namespace access control can be achieved with ClusterRole and ClusterRoleBinding, granting permissions across multiple namespaces. This is often used for service accounts or users that need to access resources in different namespaces.
Complex access policies can be designed by combining multiple Role or ClusterRole objects with RoleBinding or ClusterRoleBinding objects. These RBAC policies can include various resources and actions to provide fine grained access control that aligns with broader security requirements.
Kubernetes RBAC can be integrated with corporate security policies to align access controls within the Kubernetes environment with broader organizational security standards. This includes mapping corporate roles and permissions to Kubernetes RBAC roles and bindings to enforce consistent security postures across all platforms. This integration requires identifying the minimum necessary privileges for each role within the organization and translating these into Kubernetes RBAC policies that govern access to resources.
Kubernetes RBAC can be extended by integrating with external identity providers to manage Kubernetes cluster access more efficiently and securely. This approach allows for the centralization of user authentication, enabling unified access control policies across different platforms and services.
Leveraging external identity providers also simplifies the process of onboarding and offboarding users, as permissions can be managed from a single location.
Multi-tenancy in Kubernetes can be managed by leveraging RBAC to isolate tenants and control their access to resources. This is done by assigning tenants different namespaces and creating Roles and Role Bindings within those namespaces.
In Kubernetes, a ServiceAccount is a special kind of account that can be automatically created by Kubernetes or manually created by a user for processes running in pods. It provides an identity for carrying out actions against the Kubernetes API version. The ServiceAccount name uniquely identifies it within a namespace. An example of a ServiceAccount name in a YAML file is my-service-account.
External user groups can be synchronized with Kubernetes RBAC to streamline and secure access management within Kubernetes environments. By integrating external user directories with Kubernetes, administrators can automate the process of mapping external group memberships to roles within Kubernetes RBAC. This synchronization ensures that users' access rights in Kubernetes are consistent with their organizational roles.
While Kubernetes RBAC does not include provisioning and authenticating user accounts, it does provide authorization capabilities that govern what users can do in a Kubernetes cluster. In Kubernetes, the authorization mode RBAC is a method used to regulate access to resources within the cluster. It allows administrators to dynamically configure policies through the Kubernetes API to control users’ access to resources and what actions can be performed.
Permissions are granted to identities that are managed with Roles and ClusterRoles, which include associated access policies. A Kubernetes RBAC policy consists of the following.
When a Kubernetes API server (kube apiserver) receives a request from a person, serviceaccount, or connected device (thing), the request follows this flow.
When used in conjunction with a Cloud IAM, Kubernetes RBAC comes into play at the end of the process. Kubernetes RBAC focuses on controlling interactions specifically within Kubernetes resources according to RBAC roles. The flow for this is as follows.
Many roles can grant similar privileges in different ways. This creates challenges when a privilege needs to be revoked, as it can be difficult to ascertain which roles are applicable.
RBAC in Kubernetes comes with default settings that result in excessive permissions. For example, the bindings in the system:unauthenticated group allows an anonymous user to contact the API server through the network. Also, the automountServiceAccountToken setting is set to mount service account tokens by default.
It is possible to over permission via the permission to create workloads in a namespace, which carries with it permissions to Secrets, ConfigMaps, PersistentVolumes (see below), or even API access levels for any service account in a namespace. This can further lead to privilege escalation.
Granting unrestricted access to create a persistent volume in Kubernetes allows for the creation of hostPath volumes that give the pod access to the host filesystem on its node. This means it could then escalate privileges across that node.
If rights are granted to the proxy sub-resource of node objects, every node they have rights to opens an opportunity for command execution. These rights provide direct access to the Kubelet API, bypassing audit logging and admission controls.
Role aggregation can lead to several issues, including role explosion and overly permissive access. Role explosion results from a large number of roles becoming cumbersome and difficult to manage. Overly permissive access happens when roles accumulate more privileges than necessary. Role aggregation also complicates the audit process and the ability to clearly understand each role's access rights.
Roles with missing subjects make it more difficult to keep track of which users should have access to what. Role bindings that reference non-existent roles can lead to overpermissioning if the same role name is used in the future but attached to a different set of permissions.
Assign permissions at the namespace level where possible, using RoleBindings as opposed to ClusterRoleBindings to give users rights only within a specific namespace.
Automate Kubernetes RBAC policy management and deployment across clusters. Automation tools and scripts can streamline the creation, updating, and removal of RBAC roles, role bindings, and cluster role bindings, ensuring that access controls are dynamically adjusted to meet evolving operational needs and security standards.
Incorporate RBAC into the DevSecOps practices to bolster security throughout the software development life cycle. This should include defining clear roles and responsibilities within the continuous integration/continuous deployment (CI/CD) pipeline to ensure that only authorized personnel have access to specific resources. It is also important to regularly review and update access permissions to adapt to evolving project needs and personnel changes.
Enforce the principle of least privilege, giving users the minimum permissions necessary to perform their specific roles or tasks. Start by carefully defining roles and permissions based on functions, ensuring that access is as restrictive as possible while still allowing for operational efficiency. Regularly review and adjust roles and role bindings based on changes in responsibilities or security policies. Use namespace specific roles to limit access within a Kubernetes cluster. Additionally, continuously monitor and audit role usage and permissions to identify and remediate noncompliance with the principle of least privilege.
Avoid providing wildcard permissions, especially to all resources, because this permission applies to existing object types in the cluster as well as all object types created in the future.
Limit the distribution of privileged tokens in Kubernetes by using short-lived tokens where possible, leveraging Kubernetes service accounts for automated tasks instead of distributing user tokens, and assigning the least privilege necessary for each account's duties. In addition, regularly audit token usage and permissions, revoking and rotating tokens that are no longer needed or that pose a security risk.
Establish a routine schedule for reviews to identify unused or overly permissive roles and bindings. Document changes and maintain version control of RBAC policies aid in tracking modifications and enhancing accountability within the Kubernetes cluster.
Kubernetes RBAC provides a way to define roles and map them, but it does not, on its own, provide a way to create identities (i.e., users that are mapped to roles) or authenticate users to identities.
Kubernetes RBAC is a method of authorization. It is only used for authorization and mapping authenticated user identities to their correct permission sets.
