Cloud Security Posture - Rego policies

Project structure

.
├── bundle
│   ├── compliance                         # Compliance policies
│   │   ├── cis_aws
│   │   │   ├── rules
│   │   │   │   ├── cis_1_8                # CIS AWS 1.8 rule package
│   │   │   │   │   ├── data.yaml          # Rule's metadata
│   │   │   │   │   ├── rule.rego          # Rule's rego
│   │   │   │   │   └── test.rego          # Rule's test
│   │   │   │   ...
│   │   ├── cis_eks
│   │   │   ├── rules
│   │   ├── cis_k8s
│   │   │   ├── rules
│   │   │   ├── schemas                    # Benchmark's schemas
│   │   ├── kubernetes_common
│   │   ├── lib
│   │   │   ├── common                     # Common functions and tests
│   │   │   ├── output_validations
│   │   ├── policy                         # Common audit functions per input
│   │   │   ├── kube_api
│   │   │   ...
├── cis_policies_generator
│   ├── config
│   ├── input
│   ├── src
├── dev
└── server

Local Evaluation

input.json

should contain a beat/agent output and the benchmark (not mandatory - without specifying benchmark all benchmarks will apply), e.g. k8s eks aws

{
  "type": "file",
  "benchmark": "cis_k8s",
  "sub_type": "file",
  "resource": {
    "mode": "700",
    "path": "/hostfs/etc/kubernetes/manifests/kube-apiserver.yaml",
    "owner": "etc",
    "group": "root",
    "name": "kube-apiserver.yaml",
    "gid": 20,
    "uid": 501
  }
}

Evaluate entire policy into output.json

opa eval data.main --format pretty -i input.json -b ./bundle > output.json

Evaluate findings only

opa eval data.main.findings --format pretty -i input.json -b ./bundle > output.json

Example output

{
  "result": {
    "evaluation": "failed",
    "evidence": {
      "filemode": "700"
    },
    "expected": {
      "filemode": "644"
    }
  },
  "rule": {
    "audit": "Run the below command (based on the file location on your system) on the\ncontrol plane node.\nFor example,\n```\nstat -c %a /etc/kubernetes/manifests/kube-apiserver.yaml\n```\nVerify that the permissions are `644` or more restrictive.\n",
    "benchmark": {
      "id": "cis_k8s",
      "name": "CIS Kubernetes V1.23",
      "version": "v1.0.0"
    },
    "default_value": "By default, the `kube-apiserver.yaml` file has permissions of `640`.\n",
    "description": "Ensure that the API server pod specification file has permissions of `644` or more restrictive.\n",
    "id": "6664c1b8-05f2-5872-a516-4b2c3c36d2d7",
    "impact": "None\n",
    "name": "Ensure that the API server pod specification file permissions are set to 644 or more restrictive (Automated)",
    "profile_applicability": "* Level 1 - Master Node\n",
    "rationale": "The API server pod specification file controls various parameters that set the behavior of the API server. You should restrict its file permissions to maintain the integrity of the file. The file should be writable by only the administrators on the system.\n",
    "references": "1. [https://kubernetes.io/docs/admin/kube-apiserver/](https://kubernetes.io/docs/admin/kube-apiserver/)\n",
    "remediation": "Run the below command (based on the file location on your system) on the\ncontrol plane node.\nFor example,\n```\nchmod 644 /etc/kubernetes/manifests/kube-apiserver.yaml\n```\n",
    "section": "Control Plane Node Configuration Files",
    "tags": [
      "CIS",
      "Kubernetes",
      "CIS 1.1.1",
      "Control Plane Node Configuration Files"
    ],
    "version": "1.0"
  }
}

Evaluate with input schema

opa eval data.main --format pretty -i input.json -b ./bundle -s bundle/compliance/cis_k8s/schemas/input_schema.json
1 error occurred: bundle/compliance/lib/data_adapter.rego:11: rego_type_error: undefined ref: input.filenames
        input.filenames
              ^
              have: "filenames"
              want (one of): ["command" "filename" "gid" "mode" "path" "type" "uid"]

Local Testing

Test entire policy

opa build -b ./bundle -e ./bundle/compliance

opa test -b bundle.tar.gz -v

Test specific rule

opa test -v bundle/compliance/kubernetes_common bundle/compliance/lib bundle/compliance/cis_k8s/test_data.rego bundle/compliance/cis_k8s/rules/cis_1_1_2 --ignore="common_tests.rego"

Pre-commit hooks

see pre-commit package

• Install the package brew install pre-commit
• Then run pre-commit install
• Finally pre-commit run --all-files --verbose

Running opa server with the compliance policy

docker run --rm -p 8181:8181 -v $(pwd):/bundle openpolicyagent/opa:0.36.1 run -s -b /bundle

Test it 🚀

curl --location --request POST 'http://localhost:8181/v1/data/main' \
--header 'Content-Type: application/json' \
--data-raw '{
    "input": {
        "type": "file",
        "resource": {
            "type": "file",
            "mode": "700",
            "path": "/hostfs/etc/kubernetes/manifests/kube-apiserver.yaml",
            "uid": "etc",
            "name": "kube-apiserver.yaml",
            "group": "root"
        }
    }
}'