undermybelt Implementing RBAC Hardening for Kubernetes
Overview
Kubernetes RBAC regulates access to cluster resources based on roles assigned to users, groups, and service accounts. Default configurations often grant excessive permissions, and without active hardening, RBAC becomes a primary attack vector for privilege escalation, lateral movement, and data exfiltration. Hardening requires implementing least-privilege principles, eliminating unnecessary ClusterRole bindings, separating service accounts, integrating external identity providers, and continuous auditing.
When to Use
- When deploying or configuring implementing rbac hardening for kubernetes capabilities in your environment
- When establishing security controls aligned to compliance requirements
- When building or improving security architecture for this domain
- When conducting security assessments that require this implementation
Prerequisites
- Kubernetes cluster v1.24+ with RBAC enabled (default since v1.6)
- kubectl access with cluster-admin for initial audit
- External identity provider (OIDC) for user authentication
- Audit logging enabled on the API server
Core Hardening Principles
1. Eliminate cluster-admin Sprawl
Audit and remove unnecessary cluster-admin bindings:
# List all cluster-admin bindings
kubectl get clusterrolebindings -o json | jq -r '
.items[] |
select(.roleRef.name == "cluster-admin") |
"\(.metadata.name) -> \(.subjects[]? | "\(.kind)/\(.name) (\(.namespace // "cluster"))")"
'
2. Namespace-Scoped Roles Over ClusterRoles
Use Role and RoleBinding instead of ClusterRole and ClusterRoleBinding:
# Good: Namespace-scoped role
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
namespace: application
name: app-developer
rules:
- apiGroups: ["apps"]
resources: ["deployments"]
verbs: ["get", "list", "watch", "create", "update", "patch"]
- apiGroups: [""]
resources: ["pods", "pods/log"]
verbs: ["get", "list", "watch"]
- apiGroups: [""]
resources: ["configmaps"]
verbs: ["get", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
namespace: application
name: app-developer-binding
subjects:
- kind: Group
name: dev-team
apiGroup: rbac.authorization.k8s.io
roleRef:
kind: Role
name: app-developer
apiGroup: rbac.authorization.k8s.io
3. Dedicated Service Accounts Per Workload
apiVersion: v1
kind: ServiceAccount
metadata:
name: payment-processor
namespace: payments
automountServiceAccountToken: false # Disable auto-mount
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: payment-processor
namespace: payments
spec:
template:
spec:
serviceAccountName: payment-processor
automountServiceAccountToken: true # Only mount when explicitly needed
containers:
- name: processor
image: payments/processor:v2.1@sha256:abc...
4. Restrict Dangerous Permissions
Block permissions that enable privilege escalation:
# Dangerous verbs/resources to restrict:
# - secrets: get, list, watch (exposes all secrets in namespace)
# - pods/exec: create (enables command execution in pods)
# - pods: create with privileged securityContext
# - serviceaccounts/token: create (generates new tokens)
# - clusterroles/clusterrolebindings: create, update (self-escalation)
# - nodes/proxy: create (bypasses API server authorization)
# Safe read-only role example
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
name: security-viewer
rules:
- apiGroups: [""]
resources: ["pods", "services", "namespaces", "nodes"]
verbs: ["get", "list", "watch"]
- apiGroups: ["apps"]
resources: ["deployments", "daemonsets", "statefulsets"]
verbs: ["get", "list", "watch"]
- apiGroups: ["networking.k8s.io"]
resources: ["networkpolicies"]
verbs: ["get", "list", "watch"]
5. OIDC Integration for User Authentication
# API server flags for OIDC integration
apiVersion: v1
kind: Pod
metadata:
name: kube-apiserver
spec:
containers:
- name: kube-apiserver
command:
- kube-apiserver
- --oidc-issuer-url=https://idp.company.com
- --oidc-client-id=kubernetes
- --oidc-username-claim=email
- --oidc-groups-claim=groups
- --oidc-ca-file=/etc/kubernetes/pki/oidc-ca.crt
RBAC Audit Process
Step 1: Enumerate All Bindings
# All ClusterRoleBindings with subjects
kubectl get clusterrolebindings -o json | jq -r '
.items[] | select(.subjects != null) |
.subjects[] as $s |
"\(.metadata.name) | \(.roleRef.name) | \($s.kind)/\($s.name)"
' | sort | column -t -s '|'
# All RoleBindings across namespaces
kubectl get rolebindings --all-namespaces -o json | jq -r '
.items[] | select(.subjects != null) |
.subjects[] as $s |
"\(.metadata.namespace) | \(.metadata.name) | \(.roleRef.name) | \($s.kind)/\($s.name)"
' | sort | column -t -s '|'
Step 2: Identify Overprivileged Service Accounts
# Find service accounts with cluster-admin or admin roles
kubectl get clusterrolebindings -o json | jq -r '
.items[] |
select(.roleRef.name == "cluster-admin" or .roleRef.name == "admin") |
select(.subjects[]?.kind == "ServiceAccount") |
"\(.subjects[] | select(.kind == "ServiceAccount") | "\(.namespace)/\(.name)")"
'
Step 3: Check Default Service Account Usage
# Find pods using the default service account
kubectl get pods --all-namespaces -o json | jq -r '
.items[] |
select(.spec.serviceAccountName == "default" or .spec.serviceAccountName == null) |
"\(.metadata.namespace)/\(.metadata.name)"
'
Step 4: Verify Token Auto-Mount
# Find pods with auto-mounted service account tokens
kubectl get pods --all-namespaces -o json | jq -r '
.items[] |
select(.spec.automountServiceAccountToken != false) |
"\(.metadata.namespace)/\(.metadata.name) sa=\(.spec.serviceAccountName // "default")"
'
Tooling
rbac-lookup
# Install rbac-lookup
kubectl krew install rbac-lookup
# View RBAC for a specific user
kubectl rbac-lookup developer@company.com
# View all RBAC bindings wide format
kubectl rbac-lookup --kind user -o wide
rakkess (Review Access)
# Install rakkess
kubectl krew install access-matrix
# Show access matrix for current user
kubectl access-matrix
# Show access for a specific service account
kubectl access-matrix --sa payments:payment-processor