Terraform Plan Scanning

Evaluate Checkov Policies on Terraform Plan

Checkov supports the evaluation of policies on resources declared in .tf files. It can also be used to evaluate terraform plan expressed in a json file. Plan evaluation provides Checkov additional dependencies and context that can result in a more complete scan result. Since Terraform plan files may contain arguments (like secrets) that are injected dynamically, it is advised to run a plan evaluation using Checkov in a secure CI/CD pipeline setting.

Example

terraform init
terraform plan --out tfplan.binary
terraform show -json tfplan.binary > tfplan.json

checkov -f tfplan.json

Note: The Terraform show output file tf.json will be a single line. For that reason Checkov will report all findings as line number 0. If you have installed jq, you can convert a JSON file into multiple lines making it easier to read the scan result.

terraform show -json tfplan.binary | jq '.' > tfplan.json

checkov -f tfplan.json

The output would look like:

checkov -f tf.json
Check: CKV_AWS_21: "Ensure all data stored in the S3 bucket have versioning enabled"
	FAILED for resource: aws_s3_bucket.customer
	File: /tf/tf1.json:224-268
	Guide: https://docs.bridgecrew.io/docs/s3_16-enable-versioning

		225 |               "values": {
		226 |                 "acceleration_status": "",
		227 |                 "acl": "private",
		228 |                 "arn": "arn:aws:s3:::mybucket",

Ignored checks

Since the Terraform checks are used for both normal templates and plan files, some of those are not applicable for a plan file. They evaluate the lifecycle block, which is only relevant for the CLI and are not stored in the plan file itself.

Following checks will be ignored;

CKV_AWS_217
CKV_AWS_233
CKV_AWS_237
CKV_GCP_82

Deleted resources

To check if a resource will be deleted or changed (further change values can be found here) the change actions values can be accessed via the attribute name __change_actions__.

Ex. Python

    def scan_resource_conf(self, conf: dict[str, Any]) -> CheckResult:
        actions = conf.get("__change_actions__")
        if isinstance(actions, list) and "delete" in actions:
            return CheckResult.FAILED
        return CheckResult.PASSED

Ex. YAML

  cond_type: attribute
  resource_types:
    - aws_secretsmanager_secret
  attribute: __change_actions__
  operator: not_contains
  value: delete