Pentesting Kubernetes from the outside

There different ways to find exposed Kubernetes Pods to the internet.

Finding exposed pods with OSINT

One way could be searching for Identity LIKE "k8s.%.com" in crt.sh to find subdomains related to kubernetes. Another way might be to search "k8s.%.com" in github and search for YAML files containing the string.

Finding Exposed pods via port scanning

The following ports might be open in a Kubernetes cluster:

Port	Process	Description
443/TCP	kube-apiserver	Kubernetes API port
2379/TCP	etcd
6666/TCP	etcd	etcd
4194/TCP	cAdvisor	Container metrics
6443/TCP	kube-apiserver	Kubernetes API port
8443/TCP	kube-apiserver	Minikube API port
8080/TCP	kube-apiserver	Insecure API port
10250/TCP	kubelet	HTTPS API which allows full mode access
10255/TCP	kubelet	Unauthenticated read-only HTTP port: pods, running pods and node state
10256/TCP	kube-proxy	Kube Proxy health check server
9099/TCP	calico-felix	Health check server for Calico
6782-4/TCP	weave	Metrics and endpoints

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

Remote Cluster Misconfigurations

By default, API endpoints are forbidden to anonymous access. But it’s always a good idea to check if there are any insecure endpoints that expose sensitive information:

Checking for ETCD Anonymous Access

The ETCD stores the cluster secrets, configuration files and more sensitive data. By default, the ETCD cannot be accessed anonymously, but it always good to check.

If the ETCD can be accessed anonymously, you may need to use the etcdctl tool. The following command will get all the keys stored:

etcdctl --ndpoints=http://<MASTER-IP>:2379 get / –prefix –keys-only

Checking Kubelet (Read Only Port) Information Exposure

When the “kubelet” read-only port is exposed, the attacker can retrieve information from the API. This exposes cluster configuration elements, such as pods names, location of internal files and other configurations. This is not critical information, but it still should not be exposed to the internet.

For example, a remote attacker can abuse this by accessing the following URL: http://<external-IP>:10255/pods

References

Kubernetes Pentest Methodology Part 2CyberArk