Iac Security

---
name: iac-security
description: "Terraform, CloudFormation, and Pulumi hardening: state as a secret store, pinned providers and modules, encryption and network defaults, drift, and the privilege of the pipeline that applies the plan. Use when generating infrastructure code, reviewing IaC changes in a pull request, configuring a state backend, or setting up a new cloud account or workspace."
---

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# Infrastructure-as-Code Security

Terraform, CloudFormation, and Pulumi hardening: state as a secret store, pinned providers and modules, encryption and network defaults, drift, and the privilege of the pipeline that applies the plan. Use when generating infrastructure code, reviewing IaC changes in a pull request, configuring a state backend, or setting up a new cloud account or workspace.

## ALWAYS

- Treat the **state file as a secret store**. Every value that passes through Terraform — a generated password, an RDS master credential, a private key, the contents of a data source — is written to state in plaintext. `sensitive = true` only hides a value from CLI output; it changes nothing about what is stored. So read access to the backend is read access to those secrets, and the backend's access policy has to be written on that basis.
- Configure a **remote backend** with encryption at rest, state locking, and versioning. Prefer the backend's own locking where it exists — recent Terraform supports S3-native locking, so a separate DynamoDB lock table is no longer required for new stacks. `references/backends-and-state.md` has the per-backend form.
- Pin providers and modules to an exact version or a pessimistic constraint (`~> 5.42`), and pin a third-party module sourced from a git URL to a **commit SHA**, not a branch or tag. A module is code that runs with your apply credentials, and a registry or repository you do not control is a supply-chain input like any other.
- Give the **apply identity** the least privilege that the stack actually needs, and keep it separate from the plan identity. A pipeline role with account-wide admin turns any CI compromise into a full account compromise — `cicd-security` owns hardening the pipeline itself, `iam-best-practices` owns the role's shape.
- Encrypt persistent resources by default with a customer-managed key: object storage, block storage, managed databases, queues, log groups. Prefer a module or default that applies it, so a new resource is encrypted because of how the code is organised rather than because someone remembered.
- Deny inbound by default and open ports deliberately. Administrative and database ports reachable from `0.0.0.0/0` are the finding — SSH, RDP, and the managed database ports especially — and "it is only dev" does not change the exposure. `references/backends-and-state.md` lists the ports worth failing a build over.
- Run `plan` (or `pulumi preview`, a CloudFormation change set) in CI, require human approval before applying to production, and run scheduled **drift detection** that raises an issue when the cloud diverges from the code. Drift is where a break-glass change made at 3am quietly becomes the permanent configuration.
- Scope roles and resource policies with the provider's own condition mechanism — source account, source ARN, organization ID, TLS-only access on storage. `iam-best-practices` owns policy design; what belongs here is that the condition is expressed in the code rather than clicked into the console.

## NEVER

- Hardcode provider credentials in code or `.tfvars` (`access_key`, `secret_key`, `client_secret`, `service_account_key`). Use OIDC federation from CI, the platform's workload identity, or a secret manager.
- Commit `terraform.tfstate`, `terraform.tfstate.backup`, `.pulumi/`, or a `.tfvars` holding real values — see the state rule above for why the file is a credential dump even when the code only references variables.
- Use `local-exec` / `null_resource` to fetch a secret at apply time. It lands in state, and the provisioner runs on whatever machine ran `apply`, with that machine's identity.
- Disable provider TLS verification (`skip_tls_verify`, `insecure = true`).

## KNOWN FALSE POSITIVES

- A bastion deliberately reachable on SSH is not the same finding as a database open to the world — but "bastion" is not the exemption, its configuration is: key-only authentication, MFA, and a narrow source range. A session-manager or identity-aware-proxy path that removes the public port entirely is better than hardening one.
- Resources that are meant to be internet-facing: CDN distributions, load-balancer listeners on 80/443, API gateways, function URLs.
- Backend bootstrap resources — the bucket and lock mechanism the backend itself uses — cannot live in the state they provide. A one-time local backend that is then migrated is the normal resolution, not a finding.
- An unencrypted resource that holds nothing but public data, where the tag or classification says so explicitly.

## Reference files

Read these only when the task calls for them.

- `references/backends-and-state.md`
- `references/verifying-findings.md`