Configure Kubernetes with strong cipher suites

In a Kubernetes cluster, security is a critical aspect, and certificates play a crucial role in ensuring secure communication between various components. Here’s a brief explanation of why certificates are used in kubelet, kube-api, and related components:

kubelet:

• The kubelet is an essential component on each node in a Kubernetes cluster. It communicates with the Kubernetes master (kube-api) to manage containers and ensure they are running as expected.
• Certificates are used to authenticate the kubelet to the Kubernetes master. This helps in ensuring that only authorized nodes can join the cluster and communicate with the master.

kube-api:

• The kube-api is the API server that exposes the Kubernetes API. It serves as the entry point for managing the cluster, and receiving requests from various components (kubectl, kubelet, etc.).
• Certificates are used to authenticate clients (like kubelet) to the API server. This ensures that only authorized components can make requests to the API server.

Other Components:

• Similar principles apply to other components in the Kubernetes cluster that need to communicate securely. Certificates help in authenticating and securing communication between components to prevent unauthorized access and data tampering.

Now, regarding the drawbacks of using weak cipher suites:

Security Risks:

• Weak cipher suites can be vulnerable to various cryptographic attacks, such as brute force or man-in-the-middle attacks.
• An attacker could exploit vulnerabilities in weak ciphers to intercept, manipulate, or eavesdrop on the communication between Kubernetes components, leading to potential security breaches. (Sweet32)

Compliance Issues:

• Many security standards and compliance frameworks (such as PCI DSS, HIPAA) require the use of strong encryption algorithms. Using weak cipher suites may lead to non-compliance with these standards.

Performance Concerns:

• While strong encryption algorithms can be computationally more intensive, using weak ciphers may provide a false sense of performance improvement. In reality, the security risks associated with weak ciphers often outweigh any potential performance gains.

Limited Future Support:

• Weak ciphers are more likely to be deprecated and unsupported in the future as security standards evolve. Using outdated and insecure cryptographic algorithms may lead to maintenance challenges and potential security vulnerabilities.

In summary, using strong cipher suites is crucial for maintaining the security and integrity of communications within a Kubernetes cluster, and choosing weak ciphers can expose the cluster to various security risks and compliance issues.

kubelet

File: /var/lib/kubelet/config.yaml

Port: 10250

Add the below line to the end of the file

tlsCipherSuites: [TLS_AES_128_GCM_SHA256,TLS_AES_256_GCM_SHA384,TLS_CHACHA20_POLY1305_SHA256,TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,TLS_RSA_WITH_AES_128_CBC_SHA,TLS_RSA_WITH_AES_128_GCM_SHA256,TLS_RSA_WITH_AES_256_CBC_SHA,TLS_RSA_WITH_AES_256_GCM_SHA384]

etcd

/etc/kubernetes/manifests/etcd.yaml

add the below line in — command section

   - --cipher-suites=TLS_AES_128_GCM_SHA256,TLS_AES_256_GCM_SHA384,TLS_CHACHA20_POLY1305_SHA256,TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,TLS_RSA_WITH_AES_128_CBC_SHA,TLS_RSA_WITH_AES_128_GCM_SHA256,TLS_RSA_WITH_AES_256_CBC_SHA,TLS_RSA_WITH_AES_256_GCM_SHA384

kube-apiserver

/etc/kubernetes/manifests/kube-apiserver.yaml

add the below line in — command section

    - --tls-cipher-suites=TLS_AES_128_GCM_SHA256,TLS_AES_256_GCM_SHA384,TLS_CHACHA20_POLY1305_SHA256,TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,TLS_RSA_WITH_AES_128_CBC_SHA,TLS_RSA_WITH_AES_128_GCM_SHA256,TLS_RSA_WITH_AES_256_CBC_SHA,TLS_RSA_WITH_AES_256_GCM_SHA384

Then restart the kubelet with:-

systemctl restart kubelet

If everything looks fine, then you are good to go. Otherwise, roll back to previous.

Checking this with Nmap

nmap --script ssl-enum-ciphers -p 1-65535 <master_ip_address>

Ref:

https://kubernetes.io/docs/reference/command-line-tools-reference/kube-apiserver/#:~:text=by — cert-dir.-, — tls-cipher-suites,-strings

https://kubernetes.io/docs/reference/networking/ports-and-protocols/