alexkurd / cks

CKS

Tips after passing exam

The main problem is time. So check which questions can you do faster and choose tools according. Check beforehand allowed manuals to copy-paste templates(E.g. secrets in pods, networkpolicy, apparmor). Scroll in browser is lagging, so search the words. When you want to flag the question save result to file for later you should at least create the output file. Holding arrow buttons is just one click. Nano maybe easier for most questions, but Ctrl+W or Ctrl+Alt+W (Search text) is not working. Vi is default editor for k edit resource. Use dd to delete string. Use I instead of Insert to change mode. Vi wraps strings by default, so it's usage for falco rules is better. Trivy version is old(~0.19), so trivy k8s pods --report summary -n kube-system is not working.

Network policies

Deny all except DNS as default.

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: deny
  namespace: default
spec:
  podSelector: {}
  policyTypes:
  - Egress
  - Ingress
  egress:
  - ports:
    - port: 53
      protocol: TCP
    - port: 53
      protocol: UDP

Allow connection only between allowed selectors.

Close node metadata access (GCloud, AKS, AWS)

# all pods in namespace cannot access metadata endpoint
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: cloud-metadata-deny
  namespace: default
spec:
  podSelector: {}
  policyTypes:
  - Egress
  egress:
  - to:
    - ipBlock:
        cidr: 0.0.0.0/0
        except:
        - 169.254.169.254/32

Auto-test cluster settings for CIS recommendations

# how to run
https://github.com/aquasecurity/kube-bench/blob/main/docs/running.md
# run on master
docker run --pid=host -v /etc:/etc:ro -v /var:/var:ro -t aquasec/kube-bench:latest run --targets=master --version 1.22
# run on worker
docker run --pid=host -v /etc:/etc:ro -v /var:/var:ro -t aquasec/kube-bench:latest run --targets=node --version 1.22

Checksum binaries

RBAC

Service account mount

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
spec:
  serviceAccountName: build-robot
  automountServiceAccountToken: false
  ...

NodeRestriction

/etc/kubernetes/manifests/kube-apiserver.yaml add entry for - --enable-admission-plugins=NodeRestriction and firt Node --authorization-mode=Node

Encrypt secrets

Open policy agent(OPA)

Gatekeeper added as CRD on AdmissionController level. Create Kind.ConstraintTemplate name: k8strustedimages and add kind: K8sTrustedImages Template should describe general conditions without targets using rego syntax.

Trusted images

 violation[{"msg": msg}] {
          image := input.review.object.spec.containers[_].image
          not startswith(image, "docker.io/")
          not startswith(image, "k8s.gcr.io/")
          msg := "not trusted image!"
        }

Required labels

 violation[{"msg": msg, "details": {"missing_labels": missing}}] {
          provided := {label | input.review.object.metadata.labels[label]}
          required := {label | label := input.parameters.labels[_]}
          missing := required - provided
          count(missing) > 0
          msg := sprintf("you must provide labels: %v", [missing])
        }

Minimal replica count

violation[{"msg": msg, "details": {"missing_replicas": missing}}] {
          provided := input.review.object.spec.replicas
          required := input.parameters.min
          missing := required - provided
          missing > 0
          msg := sprintf("you must provide %v more replicas", [missing])
        }

Supply chain

Image footprint

• Make small image with minimal set of apps. Use multi-stage builds.
• Set image versions. Don't use latest.
• Set noroot user for app. // RUN addgroup -S appgroup && adduser -S appuser -G appgroup -h /home/appuser && USER appuser
• Make readonly filesystem. // RUN chmod a-w /etc
• No shell access. // RUN rm -rf /bin/*

Vulnerability scan

Clair AIO deployment with api.

Trivy

docker run ghcr.io/aquasecurity/trivy:latest image nginx:latest

Static analysis

OPA/Conftest

docker run --rm -v $(pwd):/project openpolicyagent/conftest test Dockerfile --all-namespaces

docker run --rm -v $(pwd):/project openpolicyagent/conftest test deploy.yaml

Kubesec

docker run -i kubesec/kubesec:512c5e0 scan /dev/stdin < pod.yaml

Runtime security

Strace

strace curl //create new process

strace -p pid //attach to the process

strace -p 528 -cw //collect summary

Falco

/etc/falco/rules.d

Audit logs

Add params to apiserver.yaml

    - --audit-policy-file=/etc/kubernetes/audit/policy.yaml       # add
    - --audit-log-path=/etc/kubernetes/audit/logs/audit.log       # add
    - --audit-log-maxsize=500                                     # add
    - --audit-log-maxbackup=5                                     # add
...
  volumeMounts:
  - mountPath: /etc/kubernetes/audit      # add
    name: audit                           # add
  ...
  volumes:
  - hostPath:                               # add
      path: /etc/kubernetes/audit           # add
      type: DirectoryOrCreate               # add
    name: audit                             # add