Iac Security

IaC Security

When to use

This skill reviews Infrastructure-as-Code for misconfig: over-broad IAM, public storage, missing encryption, open security groups, logging off. It leans on the cloud-provider best practices plus CIS benchmarks and orchestrates the common scanners.

Activates on:

• A request like "scan this Terraform for misconfigs", "checkov on our CloudFormation template", "is this S3 bucket policy OK", "review our Pulumi stack", "write a Conftest policy".
• New or modified IaC files: *.tf, *.tfvars, *.hcl, CloudFormation *.yaml/*.json templates, Ansible playbook.yml, roles/, Pulumi Pulumi.yaml plus __main__.py/index.ts.
• A compliance audit (ISO/SOC2/NIS2) that asks for cloud-control evidence.
• A handoff from security-review phase 3 where IaC sits in the diff.
• A drift suspicion: "is prod drifting from the Terraform state?".

When NOT to use (handoff)

• Kubernetes manifests and Helm charts → k8s-security. Even though it's IaC, K8s is its own world with its own tools.
• Dockerfile hardening → container-hardening. Image content belongs there; image-registry IAM here.
• CI pipeline hardening (the workflow that runs terraform apply) → cicd-hardening. Overlap: which creds via OIDC is mentioned here.
• Secrets in IaC files → secrets-scanner. Scan IaC with that skill before continuing here.
• Per-CVE triage on Terraform providers or modules → cve-triage.
• Cloud-runtime misconfig that doesn't come from IaC (manual console change, drift) → drift detection here, but remediation routes to ir-runbook if it's an incident.

Approach

Six phases. Phases 2 and 3 are the heart (scanning + cloud-aware review).

1. Inventory per IaC type

What do you have, in which tool, for which cloud, and what's the coverage?

• Terraform / OpenTofu: *.tf files, terraform.lock.hcl, state location (S3 + DynamoDB lock, GCS, Azure Blob, Terraform Cloud). Modules: in-house or public? Providers: which versions are pinned?
• CloudFormation: *.yaml/*.json templates, CDK output (transpiled to CFN), StackSets in multi-account setups.
• Ansible: playbooks, roles, inventory. Note: Ansible often runs against existing hosts, so IaC + runtime config are mixed.
• Pulumi: Pulumi.yaml plus language-specific code (Python/TS/Go/C#). State in Pulumi Cloud or self-hosted backend.
• Cloud-provider matrix: which providers are you touching? AWS, GCP, Azure, multi-cloud? Provider-specific tools (e.g. cfn-nag) only make sense with the matching provider.

Outcome: an overview of which IaC tech touches which cloud resources. Without that you're picking tools blind and missing the drift between tools and stacks.

2. Tool orchestration

One tool per IaC type is rarely enough; the overlap is useful because rule sets differ. Minimize to what genuinely adds value.

Terraform:

• Checkov (Prisma Cloud OSS, Apache-2). Python, broad rule set including CIS benchmarks per cloud, IaC plus container plus K8s plus secrets. Default breadth tool.
• tfsec (Aqua, MIT). Tight Terraform focus, fast. Fewer rules than Checkov but less noise. Since 2023 in maintenance mode; Trivy absorbs the rules.
• Trivy (Aqua, Apache-2). Scanner for containers, IaC, and filesystems. Useful if you already use Trivy for images.
• KICS (Checkmarx OSS). Broad IaC coverage (Terraform, CFN, K8s, Dockerfile, Ansible). Comparable to Checkov; pick one of the two.
• terrascan (Accurics, owned by Tenable). OPA-rego-based.

CloudFormation:

• cfn-lint (AWS official). Syntax and schema validation, no security rules but a required starting point.
• cfn-nag (Stelligent, MIT). Ruby, security-focused rules. Warns on IAM wildcards, open security groups, unencrypted storage.
• cfn-guard (AWS, Apache-2). Policy-as-code with its own DSL. Heavier than cfn-nag but policy-driven.
• Checkov also covers CFN; practical to combine with cfn-lint for syntax.

Ansible:

• ansible-lint (Ansible community, MIT). Best-practice plus security rules.
• KICS has Ansible rules.
• Ansible playbooks are often imperative; static analysis misses runtime state. Complement with smoke tests.

Pulumi:

• Checkov (version ≥ 2.3) supports Pulumi via state inspection.
• Policy as Code (Pulumi-native, free tier). Policy packs in the same language as the stack.
• Alternative: convert Pulumi state to a Terraform plan and scan that. Less direct.

Run tools in CI with a baseline file (see also sast-orchestrator phase 5 for noise-reduction discipline). Findings on new code are blockers; existing ones are plannable.

3. Cloud-aware review

The difference between IaC scanning and cloud review: tools catch the rules, humans catch the context. Walk these categories for every resource type that's in play.

• IAM / identity. Wildcards in Action (s3:*), wildcards in Resource (arn:aws:s3:::*), service accounts with Owner/Admin roles, cross-account trust without ExternalId, MFA not required on root or admin users. Make principle of least privilege verifiable by generating policies from CloudTrail/Audit Logs (aws iam generate-service-last-accessed-details).
• Storage. Public S3 buckets or GCS objects, default encryption off, no lifecycle policy on aging data, no versioning + MFA-delete on sensitive buckets. EBS/EFS/Azure disks unencrypted.
• Networking. Security groups with 0.0.0.0/0 on non-web ports (22 SSH, 3389 RDP, 3306 MySQL, 5432 Postgres), NACLs too permissive, route tables steering traffic via unintended paths, VPC peering without proper segmentation.
• Logging and audit. CloudTrail / Cloud Audit Logs on across all regions, logs in a separate log-archive account inaccessible to the compromise target, retention ≥ 1 year (compliance-dependent).
• Encryption. In-transit (TLS forced, RequireTLS: true on buckets, RDS forced SSL), at-rest (KMS-CMK or equivalent), key rotation on.
• Secrets. No hardcoded values in templates; reference Secrets Manager / Parameter Store / Key Vault. See secrets-scanner.
• Public exposure. Load balancers, API Gateways, App Runners, App Services: which are public? Is there a WAF in front? Geo-restrictions?

CIS benchmarks as the baseline: AWS Foundations Benchmark v3, GCP Foundation Benchmark v2, Azure Foundations Benchmark v2. All three exist as Checkov rule sets (cis_aws, cis_gcp, cis_azure).

4. Policy-as-code guardrails

Scanning is detect-after-the-fact. Policy-as-code enforces before apply.

• OPA + Conftest — Rego policies against IaC plans. terraform plan -out=tfplan && terraform show -json tfplan | conftest test -. Policies in git, reusable across stacks.
• Checkov custom policies — Python or Rego, run in the same Checkov pass.
• Terraform Sentinel (commercial, HashiCorp) — policy-as-code native in Terraform Cloud / Enterprise.
• AWS Service Control Policies (SCPs) — organization-level guardrails that IaC cannot bypass. E.g. "no region outside the EU", "no S3 ACL public-read".
• Azure Policy / GCP Organization Policy — equivalents on those platforms.

Write policies for org-specific rules tools don't know: "all databases in their own VPC", "no EC2 with public IP unless tagged public-allowed", "all S3 buckets must have object-lock on in finance accounts".

5. Drift detection

IaC state and actual cloud state can diverge through manual console changes, other tools, or compromised credentials. Without drift detection your model goes stale.

• Terraform: terraform plan in CI on a schedule, alert on non-zero diff.
• CloudFormation: Drift Detection API (aws cloudformation detect-stack-drift), wireable to CloudWatch alerts.
• Pulumi: pulumi refresh --expect-no-changes, fails on diff.
• Driftctl (OSS) — cross-provider drift detection.
• Cloudquery — declarative cloud-state extractor, match against IaC.

Drift is not by definition a security incident, but unintended drift must be triaged. On suspicious drift (a new IAM role not in code): escalate to ir-runbook.

6. Verification-loop

Layer 1: scope (every IaC type in the repo covered? all regions/accounts? drift check active?), assumptions ("CIS-benchmark compliant" backed by tool output, not eyeballed), gaps (secrets and k8s-manifests explicitly handed off?), consistency (policy-as-code rules not in conflict with SCPs).

Layer 2: CIS benchmark version numbers correct, cloud-provider feature names current (AWS changes feature names), no fabricated rule IDs from a scanner, CVE references (when used for a specific IaC misconfig) verified against NVD.

Output

IaC Security review — <scope>
IaC types: <terraform | cfn | ansible | pulumi>
Clouds in scope: <aws | gcp | azure | multi>

Scan output (summary, no raw dumps):
  Checkov:    <N blockers, M medium, K low>
  tfsec/Trivy:<...>
  cfn-nag:    <...>

Cloud-aware findings:
  IAM:         <list of overly permissive roles/policies>
  Storage:     <public buckets, unencrypted volumes>
  Networking:  <open security groups, NACL gaps>
  Logging:     <CloudTrail/audit gaps>
  Encryption:  <in-transit + at-rest gaps>

Policy-as-code status:
  Active:      <OPA/Conftest | Sentinel | SCPs | Org Policy>
  Coverage:    <which rules active, which not>

Drift:
  Last checked: <date>
  Divergence:   <none | see appendix>

Findings (severity-sorted, blockers first, follow security-review format)

Verification-loop: ...

References

• OWASP IaC Security — https://owasp.org/www-project-iac-security/. OWASP IaC Top 10 and guidance.
• CIS Benchmarks — https://www.cisecurity.org/cis-benchmarks. AWS Foundations, GCP Foundation, Azure Foundations — the baseline.
• Checkov — https://www.checkov.io/. Tool docs plus rule-set reference.
• tfsec / Trivy IaC — https://aquasecurity.github.io/trivy/latest/docs/coverage/iac/. Trivy-integrated IaC scanning.
• cfn-nag — https://github.com/stelligent/cfn_nag. CloudFormation rules.
• AWS cfn-guard — https://docs.aws.amazon.com/cfn-guard/latest/ug/what-is-guard.html.
• ansible-lint — https://ansible.readthedocs.io/projects/lint/. Lint rules including security.
• Pulumi Policy as Code — https://www.pulumi.com/docs/using-pulumi/crossguard/.
• OPA / Conftest — https://www.openpolicyagent.org/ and https://www.conftest.dev/.
• NIST SP 800-204D — https://csrc.nist.gov/pubs/sp/800/204/d/final. Strategies for secure DevSecOps.
• AWS Well-Architected Security Pillar — https://docs.aws.amazon.com/wellarchitected/latest/security-pillar/welcome.html. Primary AWS guidance.
• Google Cloud Security Best Practices — https://cloud.google.com/security/best-practices.
• Azure Security Baseline — https://learn.microsoft.com/en-us/security/benchmark/azure/.

Categories

• appsec