Terraform Plan and External Terraform Module 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",

Scanning Third-Party Terraform Modules

Third-party Terraform modules often reduce complexity for deploying services made up of many objects.

For example, the third-party EKS module by howdio reduces the terraform required to the nine lines below, however, in doing so abstracts the terraform configuration away from a regular Checkov scan on the current directory.

module "eks" {
  source = "howdio/eks/aws"

  name        = "examplecluster"
  default_vpc = true

  enable_kubectl   = true
  enable_dashboard = true
}

To ensure coverage of objects within these modules, you can instruct Checkov to scan the .terraform directory, after a terraform init, which will have retrieved the third-party modules and any associated .tf files:

terraform init
checkov -d . # Your TF files.
checkov -d .terraform # Module TF files.

It is worth noting however, that when scanning the .terraform directory, Checkov cannot differentiate between third-party and internally written modules. That said, you will benefit from scanning coverage across all of them.