Terraform AWS Service Control Policies

This repo is a collection of AWS Service Control Policies (SCPs) written in Hashicorp Terraform to be used in AWS Organizations.

About Service Control Policies

• For official documentation about SCPs, visit the links here and here.
• SCPs enable you to restrict, at the account level of granularity, what services and actions the users, groups and roles in those accounts can do.
• SCPs are available only in an organization that has all features enabled. SCPs aren't available if your organization has enabled only the consolidated billing features.

Considerations

• Best practice is to never attach SCPs to the root of your organization. Instead, create an Organizational Unit (OU) underneath root and attach policies there.
• SCPs do not grant permissions in IAM but instead allow/deny services or set security guardrails.
• Root user accounts are affected by SCPs.
• You must have at least one SCP attached to each entity.
• Maximum of 5 SCPs can be attached to the root, OU, or Account in an organization.

Permission Logic

• If a user or role has an IAM permission policy that grants access to an action that is also allowed by the applicable SCPs, the user or role can perform that action.
• If a user or role has an IAM permission policy that grants access to an action that is either not allowed or explicitly denied by the applicable SCPs, the user or role can't perform that action.
• AWS Organizations use a tree hierarchy for SCPs. This means that if your account is in an Organizational Unit, it inherits that OUs policies.
• From the documentation:

Content

• The security_controls_scp folder is a modularized grouping of AWS Security Best Practices to control at the AWS Organizations level.
  • NOTICE: Due to the limitations of Service Control Policies, only a max of 5 may be attached at one time. With that in mind, you cannot apply ALL of the security controls at once (in their current modularized format). All of the SCPs will attempt to attach to one target ID and will fail. You have a couple of options:
    • Select the aws_iam_policy_document you want and combine into one large data document.
    • Pick and choose 5 modules to deploy and remove the others.
    • Remove aws_organizations_policy_attachment from the modules' main.tf file and apply. You would then need to manually attach the SCPs.
• The compliance_scp folder is a collection of compliance-flavored SCPs. These SCPs only allow AWS services that are compliant with the respective compliance framework. All SCP JSON files are sourced from Salesforce's aws-allowlister repository which updates via a weekly cronjob.

Usage

An example main.tf for the module to deny the ability to delete CloudTrail Trails:

module "cloudtrail" {
  source      = "./modules/cloudtrail"

  target_id = "123456789012"
  aws_region = "us-east-1"
  shared_credentials_file = "~/.aws/credentials"
  customprofile = "default"
}

Deployment

To Deploy all of the AWS security best practice SCPs navigate to security_controls_scp:

• terraform init to get the plugins.
• terraform plan to verify your resource planning.
• terraform apply to apply your SCPs.

You will receive an error related similar to ConstraintViolationException: You have attached the maximum number of policies to the specified target. when you deploy ALL of the security related SCPs. We recommend only deploying the SCPs you need by leveraging the -target flag in your terraform apply command. An example command to deploy only the S3 and Lambda SCPs is below:

• terraform apply -target=module.s3 -target=module.lambda

To Remove the SCPs:

• terraform destroy to destroy the deployed policies.

Deployment Dependencies

• Terraform v12
• terraform-provider-aws
• An AWS Organization
• An IAM user with Organization Admin Access

Common Errors

Enabled Policy Types

error creating Organizations Policy Attachment: PolicyTypeNotEnabledException: This operation can be performed only for enabled policy types.
status code: 400, request id: 2b8ecgeb-34h3-11e6-86fb-275c76986dec

SCP functionality must be enabled on the root. See hashicorp/terraform-provider-aws#4545 for more information

Minimum SCP Requirement

aws_organizations_policy_attachment.deny_orgs_leave_attachment: ConstraintViolationException: You cannot remove the last policy attached to the specified target. You must have at least one attached at all times.
status code: 400, request id: 2d6c75b3-5757-13e9-ab76-518b756aebd3

You must have one SCP attached to an account or OU at all times. See: https://docs.aws.amazon.com/organizations/latest/userguide/orgs_reference_limits.html for more information.

Conflicting Policy Attachment

error creating Organizations Policy Attachment: ConcurrentModificationException: AWS Organizations can't complete your request because it conflicts with another attempt to modify the same entity. Try again later. status code: 400, request id: h725f9g7-1234-12e9-h746-ch123ab12345

Occasionally, if you try to assign many SCPs to one target at the same time, it could error out. If you see this error simply run terraform apply again.

Limitation of Liability

Please view the License for limitations of liability.