Scanning Kubernetes Manifests with Kubesec Skill

Scanning Kubernetes Manifests with Kubesec

Overview

Kubesec is an open-source security risk analysis tool developed by ControlPlane that inspects Kubernetes resource manifests for common exploitable risks such as privilege escalation, writable host mounts, and excessive capabilities. It assigns a numerical security score to each resource and provides actionable recommendations for hardening. Kubesec can be used as a CLI binary, Docker container, kubectl plugin, admission webhook, or REST API endpoint.

When to Use

When conducting security assessments that involve scanning kubernetes manifests with kubesec
When following incident response procedures for related security events
When performing scheduled security testing or auditing activities
When validating security controls through hands-on testing

Prerequisites

Kubernetes manifest files (YAML/JSON) for Deployments, Pods, DaemonSets, StatefulSets
Docker or Go runtime for local installation
kubectl access for scanning live cluster resources
CI/CD pipeline access for automated scanning integration

Core Concepts

Security Scoring System

Kubesec assigns a score to each Kubernetes resource based on security checks:

Positive scores: Awarded for security-enhancing configurations (readOnlyRootFilesystem, runAsNonRoot)
Zero or negative scores: Indicate missing security controls or dangerous configurations
Critical advisories: Flagged configurations that represent immediate security risks

Check Categories

Privilege Controls: Checks for privileged containers, host PID/network access, root execution
Capabilities: Identifies excessive Linux capabilities (SYS_ADMIN, NET_RAW)
Volume Mounts: Detects dangerous host path mounts and writable sensitive paths
Resource Limits: Validates presence of CPU/memory resource constraints
Security Context: Verifies seccomp profiles, AppArmor annotations, SELinux contexts

Installation

Binary Installation

# Linux/macOS
curl -sSL https://github.com/controlplaneio/kubesec/releases/latest/download/kubesec_linux_amd64.tar.gz | \
  tar xz -C /usr/local/bin/ kubesec

# Verify installation
kubesec version

Docker Installation

docker pull kubesec/kubesec:v2

# Scan a manifest file
docker run -i kubesec/kubesec:v2 scan /dev/stdin < deployment.yaml

kubectl Plugin

kubectl krew install kubesec-scan
kubectl kubesec-scan pod mypod -n default

Practical Scanning

Scanning a Single Manifest

# Scan a deployment manifest
kubesec scan deployment.yaml

# Scan with JSON output
kubesec scan -o json deployment.yaml

# Scan from stdin
cat pod.yaml | kubesec scan -

Sample Output

[
  {
    "object": "Pod/web-app.default",
    "valid": true,
    "fileName": "pod.yaml",
    "message": "Passed with a score of 3 points",
    "score": 3,
    "scoring": {
      "passed": [
        {
          "id": "ReadOnlyRootFilesystem",
          "selector": "containers[] .securityContext .readOnlyRootFilesystem == true",
          "reason": "An immutable root filesystem prevents applications from writing to their local disk",
          "points": 1
        },
        {
          "id": "RunAsNonRoot",
          "selector": "containers[] .securityContext .runAsNonRoot == true",
          "reason": "Force the running image to run as a non-root user",
          "points": 1
        },
        {
          "id": "LimitsCPU",
          "selector": "containers[] .resources .limits .cpu",
          "reason": "Enforcing CPU limits prevents DOS via resource exhaustion",
          "points": 1
        }
      ],
      "advise": [
        {
          "id": "ApparmorAny",
          "selector": "metadata .annotations .\"container.apparmor.security.beta.kubernetes.io/nginx\"",
          "reason": "Well defined AppArmor policies reduce the attack surface of the container",
          "points": 3
        },
        {
          "id": "ServiceAccountName",
          "selector": ".spec .serviceAccountName",
          "reason": "Service accounts restrict Kubernetes API access and should be configured",
          "points": 3
        }
      ]
    }
  }
]

Scanning Multiple Resources

# Scan all YAML files in a directory
for file in manifests/*.yaml; do
  echo "=== Scanning $file ==="
  kubesec scan "$file"
done

# Scan multi-document YAML
kubesec scan multi-resource.yaml

Using the HTTP API

# Scan via the public API
curl -sSX POST --data-binary @deployment.yaml \
  https://v2.kubesec.io/scan

# Run a local API server
kubesec http --port 8080 &

# Scan against local server
curl -sSX POST --data-binary @deployment.yaml \
  http://localhost:8080/scan

CI/CD Integration

GitHub Actions

name: Kubesec Scan
on: [pull_request]
jobs:
  kubesec:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Install Kubesec
        run: |
          curl -sSL https://github.com/controlplaneio/kubesec/releases/latest/download/kubesec_linux_amd64.tar.gz | \
            tar xz -C /usr/local/bin/ kubesec
      - name: Scan Manifests
        run: |
          FAIL=0
          for file in k8s/*.yaml; do
            SCORE=$(kubesec scan "$file" | jq '.[0].score')
            echo "$file: score=$SCORE"
            if [ "$SCORE" -lt 0 ]; then
              echo "FAIL: $file has critical issues (score: $SCORE)"
              FAIL=1
            fi
          done
          exit $FAIL

GitLab CI

kubesec-scan:
  stage: security
  image: kubesec/kubesec:v2
  script:
    - |
      for file in k8s/*.yaml; do
        kubesec scan "$file" > /tmp/result.json
        SCORE=$(cat /tmp/result.json | jq '.[0].score')
        if [ "$SCORE" -lt 0 ]; then
          echo "CRITICAL: $file scored $SCORE"
          cat /tmp/result.json | jq '.[0].scoring.critical'
          exit 1
        fi
      done
  artifacts:
    paths:
      - kubesec-results/

Admission Webhook

Deploy Kubesec as a ValidatingWebhookConfiguration to reject insecure manifests at deploy time:

apiVersion: admissionregistration.k8s.io/v1
kind: ValidatingWebhookConfiguration
metadata:
  name: kubesec-webhook
webhooks:
  - name: kubesec.controlplane.io
    rules:
      - apiGroups: [""]
        apiVersions: ["v1"]
        operations: ["CREATE", "UPDATE"]
        resources: ["pods"]
      - apiGroups: ["apps"]
        apiVersions: ["v1"]
        operations: ["CREATE", "UPDATE"]
        resources: ["deployments", "daemonsets", "statefulsets"]
    clientConfig:
      service:
        name: kubesec-webhook
        namespace: kube-system
        path: /scan
    failurePolicy: Fail
    sideEffects: None
    admissionReviewVersions: ["v1"]

Security Checks Reference

Critical Checks (Negative Score)

| Check | Selector | Risk | |-------|----------|------| | Privileged | securityContext.privileged == true | Full host access | | HostPID | spec.hostPID == true | Process namespace escape | | HostNetwork | spec.hostNetwork == true | Network namespace escape | | SYS_ADMIN | capabilities.add contains SYS_ADMIN | Near-root capability |

Best Practice Checks (Positive Score)

| Check | Points | Description | |-------|--------|-------------| | ReadOnlyRootFilesystem | +1 | Prevents filesystem writes | | RunAsNonRoot | +1 | Non-root process execution | | RunAsUser > 10000 | +1 | High UID reduces collision risk | | LimitsCPU | +1 | Prevents CPU resource exhaustion | | LimitsMemory | +1 | Prevents memory resource exhaustion | | RequestsCPU | +1 | Ensures scheduler resource awareness | | ServiceAccountName | +3 | Explicit service account | | AppArmor annotation | +3 | Kernel-level MAC enforcement | | Seccomp profile | +4 | Syscall filtering |

Agent Skills: Scanning Kubernetes Manifests with Kubesec

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