5 min read

Kubernetes Security: How Can We Secure a Kubernetes Cluster?

In my childhood, my uncle used to ask me to secure our small rice mill. I would always ask, “What am I securing, and from whom?” 🤔
This early lesson in threat modeling now echoes in my approach to Kubernetes security.

Just like securing that rice mill, securing a Kubernetes cluster starts with understanding what needs protection—and from what threats .

We will find our first answer on what are we actually securing in Kubernetes?

Understanding the Security Layers of Kubernetes

Kubernetes is an ecosystem with multiple layers, and security must be approached holistically. The three key layers are:

1. The Infrastructure – The cloud or on-premises environment hosting the Kubernetes cluster.
2. The Kubernetes Cluster – The control plane, API server, kubelet, and etcd.
3. The Applications – The containers, Pods, and services running within the cluster.

I say it a 3 leg pillars and we need to plan to fill the security gap for all these 3 legs to secure the cluster holistically

Each of these layers presents unique vulnerabilities, and securing Kubernetes means protecting all three.

1. Secure Your Container Images (Kubernetes Security Starts Here)

Everything in Kubernetes starts with containers, which are built from images. If an image is compromised, the entire cluster is at risk.

Default Kubernetes Behavior

• Kubernetes does not verify image security by default.
• Users can pull images from any registry, including any unsafe sources.

Best Practices for Image Security

✅ Scan Images for Vulnerabilities – Use tools like Trivy, Clair, or Anchore during CI in the DevOps Pipeline.

✅ Use Signed & Trusted Images – Store images in a private registry.

✅ Run Containers as Non-Root – Prevent privilege escalation by enforcing securityContext settings.

2. Protect Pods & Containers from Runtime Threats

Even a secure image can become a security risk once running inside a cluster. A compromised Pod can be used to steal data, escalate privileges, or move laterally within the cluster.

Default Kubernetes Behavior

• Pods run as root by default, allowing them to access the host.

kubectl exec -it pod_name -- /bin/bash && id

• Kubernetes does not automatically restrict access to sensitive files or networks.

Best Practices for Pod Security

✅ Set Security Contexts – Configure runAsNonRoot: true and allowPrivilegeEscalation: false.

✅ Restrict Host Access – Avoid hostPID: true and hostNetwork: true.

✅ Use Pod Security Admission (PSA) – Enforce strict policies on Pod execution.

3. Implement Role-Based Access Control (RBAC) Properly

One of the biggest threats to Kubernetes is misconfigured access control. If an attacker gains admin-level access, they can control the entire cluster.

Default Kubernetes Behavior

• Every Pod gets a default service account, which may have unnecessary permissions.
• Many clusters have overly permissive Role-Based Access Control (RBAC).

Best Practices for Access Control

✅ Apply Least Privilege – Use RBAC to grant only necessary permissions.

✅ Disable Default Service Accounts – Prevent automatic mounting of service account tokens.

✅ Audit Role Bindings – Regularly review users and service accounts with cluster-admin privileges.

4. Control Pod-to-Pod Communication with Network Policies

By default, all Pods in a cluster can talk to each other, creating a major risk. If an attacker compromises one Pod, they can access other sensitive services.

Default Kubernetes Behavior

• No network restrictions exist between Pods.
• Traffic within the cluster is unencrypted.

Best Practices for Network Security

✅ Use Network Policies – Define which Pods can communicate with others.

✅ Implement Service Mesh (Istio, Linkerd) – Enforce traffic control and mutual TLS encryption.

✅ Enable mTLS – Encrypt internal communication between services.

5. Safeguard Kubernetes Secrets & Sensitive Data

Applications running in Kubernetes often require API keys, database credentials, and tokens. If these secrets are stored in plain text, they can easily be leaked.

Default Kubernetes Behavior

• Kubernetes stores secrets base64-encoded, not encrypted using any symmetric key.
• Any Pod with access to a Secret can read it.

Best Practices for Secret Management

✅ Use External Secret Management – Use AWS KMS, HashiCorp Vault, or Azure Key Vault.

✅ Encrypt Secrets at Rest – Enable etcd encryption.

✅ Restrict Secret Access – Apply RBAC rules to limit exposure.

6. Harden Your etcd & Cluster Configuration

etcd is the central database for Kubernetes, it stores everything from cluster configurations to API server credentials. If an attacker gains access, they can modify cluster state and steal sensitive data.

Default Kubernetes Behavior

• etcd data is not encrypted by default.
• etcd is often exposed on the network, making it a target.

Best Practices for etcd Security

✅ Enable etcd Encryption – Use –encryption-provider-config.

✅ Restrict etcd Access – Ensure only the API server can communicate with etcd.

✅ Backup etcd Regularly – Prevent data loss due to corruption or attack.

7. Enforce Kubernetes Security Policies with Kyverno or OPA

Even with best practices in place, misconfigurations can happen. Automated security policy enforcement can prevent bad configurations from entering the cluster.

Default Kubernetes Behavior

• Kubernetes does not enforce security policies by default.
• Users can create insecure resources without restrictions.

Best Practices for Policy Enforcement

✅ Use Kyverno or OPA Gatekeeper – Prevent misconfigurations before deployment.

✅ Enforce Security Policies – Require non-root containers, encrypted secrets, and minimal privileges.

✅ Automate Compliance Checks – Continuously validate security best practices.

Though we have discussed and pointed few points above, but we need to realise that securing Kubernetes is not about a single solution, it’s about applying multiple layers of defense. Finally we should always keep the CIS benchmark in mind while we think about securing the Kubernetes.

f you’re looking to assess your current Kubernetes setup, Lia Infraservices offers detailed Security & Compliance Audits to help identify vulnerabilities and strengthen your cluster’s defenses. To align with industry standards, refer to the Kubernetes CIS Benchmarks and explore the official Kubernetes documentation on security for comprehensive guidance.