# Exposing Services in Kubernetes {% hint style="success" %} Learn & practice AWS Hacking:[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)\ Learn & practice GCP Hacking: [**HackTricks Training GCP Red Team Expert (GRTE)**](https://training.hacktricks.xyz/courses/grte)
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{% endhint %} There are **different ways to expose services** in Kubernetes so both **internal** endpoints and **external** endpoints can access them. This Kubernetes configuration is pretty critical as the administrator could give access to **attackers to services they shouldn't be able to access**. ### Automatic Enumeration Before starting enumerating the ways K8s offers to expose services to the public, know that if you can list namespaces, services and ingresses, you can find everything exposed to the public with: ```bash kubectl get namespace -o custom-columns='NAME:.metadata.name' | grep -v NAME | while IFS='' read -r ns; do echo "Namespace: $ns" kubectl get service -n "$ns" kubectl get ingress -n "$ns" echo "==============================================" echo "" echo "" done | grep -v "ClusterIP" # Remove the last '| grep -v "ClusterIP"' to see also type ClusterIP ``` ### ClusterIP A **ClusterIP** service is the **default** Kubernetes **service**. It gives you a **service inside** your cluster that other apps inside your cluster can access. There is **no external access**. However, this can be accessed using the Kubernetes Proxy: ```bash kubectl proxy --port=8080 ``` Now, you can navigate through the Kubernetes API to access services using this scheme: `http://localhost:8080/api/v1/proxy/namespaces//services/:/` For example you could use the following URL: `http://localhost:8080/api/v1/proxy/namespaces/default/services/my-internal-service:http/` to access this service: ```yaml apiVersion: v1 kind: Service metadata: name: my-internal-service spec: selector: app: my-app type: ClusterIP ports: - name: http port: 80 targetPort: 80 protocol: TCP ``` _This method requires you to run `kubectl` as an **authenticated user**._ List all ClusterIPs: {% code overflow="wrap" %} ```bash kubectl get services --all-namespaces -o=custom-columns='NAMESPACE:.metadata.namespace,NAME:.metadata.name,TYPE:.spec.type,CLUSTER-IP:.spec.clusterIP,PORT(S):.spec.ports[*].port,TARGETPORT(S):.spec.ports[*].targetPort,SELECTOR:.spec.selector' | grep ClusterIP ``` {% endcode %} ### NodePort When **NodePort** is utilised, a designated port is made available on all Nodes (representing the Virtual Machines). **Traffic** directed to this specific port is then systematically **routed to the service**. Typically, this method is not recommended due to its drawbacks. List all NodePorts: {% code overflow="wrap" %} ```bash kubectl get services --all-namespaces -o=custom-columns='NAMESPACE:.metadata.namespace,NAME:.metadata.name,TYPE:.spec.type,CLUSTER-IP:.spec.clusterIP,PORT(S):.spec.ports[*].port,NODEPORT(S):.spec.ports[*].nodePort,TARGETPORT(S):.spec.ports[*].targetPort,SELECTOR:.spec.selector' | grep NodePort ``` {% endcode %} An example of NodePort specification: ```yaml apiVersion: v1 kind: Service metadata: name: my-nodeport-service spec: selector: app: my-app type: NodePort ports: - name: http port: 80 targetPort: 80 nodePort: 30036 protocol: TCP ``` If you **don't specify** the **nodePort** in the yaml (it's the port that will be opened) a port in the **range 30000–32767 will be used**. ### LoadBalancer Exposes the Service externally **using a cloud provider's load balancer**. On GKE, this will spin up a [Network Load Balancer](https://cloud.google.com/compute/docs/load-balancing/network/) that will give you a single IP address that will forward all traffic to your service. In AWS it will launch a Load Balancer. You have to pay for a LoadBalancer per exposed service, which can be expensive. List all LoadBalancers: {% code overflow="wrap" %} ```bash kubectl get services --all-namespaces -o=custom-columns='NAMESPACE:.metadata.namespace,NAME:.metadata.name,TYPE:.spec.type,CLUSTER-IP:.spec.clusterIP,EXTERNAL-IP:.status.loadBalancer.ingress[*],PORT(S):.spec.ports[*].port,NODEPORT(S):.spec.ports[*].nodePort,TARGETPORT(S):.spec.ports[*].targetPort,SELECTOR:.spec.selector' | grep LoadBalancer ``` {% endcode %} ### External IPs {% hint style="success" %} External IPs are exposed by services of type Load Balancers and they are generally used when an external Cloud Provider Load Balancer is being used. For finding them, check for load balancers with values in the `EXTERNAL-IP` field. {% endhint %} Traffic that ingresses into the cluster with the **external IP** (as **destination IP**), on the Service port, will be **routed to one of the Service endpoints**. `externalIPs` are not managed by Kubernetes and are the responsibility of the cluster administrator. In the Service spec, `externalIPs` can be specified along with any of the `ServiceTypes`. In the example below, "`my-service`" can be accessed by clients on "`80.11.12.10:80`" (`externalIP:port`) ```yaml apiVersion: v1 kind: Service metadata: name: my-service spec: selector: app: MyApp ports: - name: http protocol: TCP port: 80 targetPort: 9376 externalIPs: - 80.11.12.10 ``` ### ExternalName [**From the docs:**](https://kubernetes.io/docs/concepts/services-networking/service/#externalname) Services of type ExternalName **map a Service to a DNS name**, not to a typical selector such as `my-service` or `cassandra`. You specify these Services with the `spec.externalName` parameter. This Service definition, for example, maps the `my-service` Service in the `prod` namespace to `my.database.example.com`: ```yaml apiVersion: v1 kind: Service metadata: name: my-service namespace: prod spec: type: ExternalName externalName: my.database.example.com ``` When looking up the host `my-service.prod.svc.cluster.local`, the cluster DNS Service returns a `CNAME` record with the value `my.database.example.com`. Accessing `my-service` works in the same way as other Services but with the crucial difference that **redirection happens at the DNS level** rather than via proxying or forwarding. List all ExternalNames: {% code overflow="wrap" %} ```bash kubectl get services --all-namespaces | grep ExternalName ``` {% endcode %} ### Ingress Unlike all the above examples, **Ingress is NOT a type of service**. Instead, it sits **in front of multiple services and act as a “smart router”** or entrypoint into your cluster. You can do a lot of different things with an Ingress, and there are **many types of Ingress controllers that have different capabilities**. The default GKE ingress controller will spin up a [HTTP(S) Load Balancer](https://cloud.google.com/compute/docs/load-balancing/http/) for you. This will let you do both path based and subdomain based routing to backend services. For example, you can send everything on foo.yourdomain.com to the foo service, and everything under the yourdomain.com/bar/ path to the bar service. The YAML for a Ingress object on GKE with a [L7 HTTP Load Balancer](https://cloud.google.com/compute/docs/load-balancing/http/) might look like this: ```yaml apiVersion: extensions/v1beta1 kind: Ingress metadata: name: my-ingress spec: backend: serviceName: other servicePort: 8080 rules: - host: foo.mydomain.com http: paths: - backend: serviceName: foo servicePort: 8080 - host: mydomain.com http: paths: - path: /bar/* backend: serviceName: bar servicePort: 8080 ``` List all the ingresses: {% code overflow="wrap" %} ```bash kubectl get ingresses --all-namespaces -o=custom-columns='NAMESPACE:.metadata.namespace,NAME:.metadata.name,RULES:spec.rules[*],STATUS:status' ``` {% endcode %} Although in this case it's better to get the info of each one by one to read it better: ```bash kubectl get ingresses --all-namespaces -o=yaml ``` ### References * [https://medium.com/google-cloud/kubernetes-nodeport-vs-loadbalancer-vs-ingress-when-should-i-use-what-922f010849e0](https://medium.com/google-cloud/kubernetes-nodeport-vs-loadbalancer-vs-ingress-when-should-i-use-what-922f010849e0) * [https://kubernetes.io/docs/concepts/services-networking/service/](https://kubernetes.io/docs/concepts/services-networking/service/) {% hint style="success" %} Learn & practice AWS Hacking:[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)\ Learn & practice GCP Hacking: [**HackTricks Training GCP Red Team Expert (GRTE)**](https://training.hacktricks.xyz/courses/grte)
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