IAM Policy Validator for Terraform

A command line tool that takes a Terraform template, parses IAM identity-based and resource-based policies, then runs them through IAM Access Analyzer policy validation checks and (optionally) through IAM Access Analyzer custom policy checks. Note that a charge is associated with each custom policy check. For more details about pricing, see IAM Access Analyzer pricing.

Table of Contents

• Pre-requisites
• Getting Started
• Limitations
• Frequently Asked Questions
• Contributors

Pre-requisites

An analyzer needs to exist in the account. To create an analyzer with the account as the zone of trust, see AWS documentation here.

Getting Started

Installation

Python 3+ is supported.

$ pip install tf-policy-validator
$ tf-policy-validator -h

Credentials

The tool should be run using credentials from the AWS account that you plan to deploy terraform template to. The tool uses boto3 to interact with your AWS account. You can use one of the following methods to specify credentials:

• Environment variables
• Shared credential file (~/.aws/credentials)
• AWS config file (~/.aws/config)
• Assume Role provider
• Instance metadata service on an Amazon EC2 instance that has an IAM role configured.

Read more about these options

The principal used to execute the tool requires the following permissions.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AccessAnalyzerValidatePolicy",
            "Effect": "Allow",
            "Action": [
                "access-analyzer:ValidatePolicy",
                "access-analyzer:CheckNoNewAccess",
                "access-analyzer:CheckAccessNotGranted",
                "access-analyzer:CheckNoPublicAccess"
            ],
            "Resource": "*"
        }
    ]
}

Action Name	Justificiation
access-analyzer:ValidatePolicy	Called for each policy to validate against IAM policy best practices.
access-analyzer:CheckNoNewAccess	Called for each policy to validate against a reference policy to compare permissions.
access-analyzer:CheckAccessNotGranted	Called for each policy to validate that it does not grant access to a list of IAM actions, considered as critical permissions, provided as input.
access-analyzer:CheckNoPublicAccess	Called for each policy to validate that it does not grant public access to supported resource types.

Basic usage

tf-policy-validator validate --config iam_check/config/default.yaml --template-path ./my-template.json --region us-east-1

Commands

validate

tf-policy-validator validate --config iam_check/config/default.yaml --template-path ./my-template.json --region us-east-1

Parses IAM identity-based and resource-based policies from Terraform templates. Then runs the policies through IAM Access Analyzer for validation. Returns the findings from validation in JSON format. Exits with a non-zero error code if any findings categorized as blocking are found in your template. Exits with an error code of zero if all findings are non-blocking or there are no findings.

Arguments	Required	Options	Description
--help			show this help message and exit
--template-path		FILE_NAME	The path to the Terraform plan file (JSON).
--region	Yes	REGION	The destination region the resources will be deployed to.
--profile		PROFILE	The named profile to use for AWS API calls.
--enable-logging			Enables log output to stdout
--ignore-finding		FINDING_CODE, RESOURCE_NAME, RESOURCE_NAME.FINDING_CODE	Allow validation failures to be ignored. Specify as a comma separated list of findings to be ignored. Can be individual finding codes (e.g. "PASS_ROLE_WITH_STAR_IN_RESOURCE"), a specific resource name (e.g. "MyResource"), or a combination of both separated by a period.(e.g. "MyResource.PASS_ROLE_WITH_STAR_IN_RESOURCE"). Names of finding codes may change in IAM Access Analyzer over time.
--treat-finding-type-as-blocking		ERROR, SECURITY_WARNING, WARNING, SUGGESTION, NONE	Specify which finding types should be treated as blocking. Other finding types are treated as nonblocking. If the tool detects any blocking finding types, it will exit with a non-zero exit code. If all findings are nonblocking or there are no findings, the tool exits with an exit code of 0. Defaults to "ERROR" and "SECURITY_WARNING". Specify as a comma separated list of finding types that should be blocking. Pass "NONE" to ignore all findings.
--allow-external-principals		ACCOUNT,ARN	A comma separated list of external principals that should be ignored. Specify as a comma separated list of a 12 digit AWS account ID, a federated web identity user, a federated SAML user, or an ARN. Specify "*" to allow anonymous access. (e.g. 123456789123,arn:aws:iam::111111111111:role/MyOtherRole,graph.facebook.com)
--config	Yes	FILE_NAME1, FILE_NAME2, ...	A list of config files for running this script
check-no-new-access

tf-policy-validator check-no-new-access --config iam_check/config/default.yaml --template-path iam_check/test/test_policy_accessanalyzer.json --region us-west-2 --reference-policy-type identity --reference-policy iam_check/test/test_policy.json

Parses IAM identity-based and resource-based policies from Terraform templates. Then runs the policies through IAM Access Analyzer for a custom check against a reference policy. Returns the findings from the custom check in JSON format. Exits with a non-zero error code if any findings categorized as blocking, based on new access, are found in your template. Exits with an error code of zero if all findings are non-blocking or there are no findings. You can find examples for reference policies and learn how to set up and run a custom policy check for new access in the IAM Access Analyzer custom policy checks samples repository on GitHub.

Arguments	Required	Options	Description
--help			show this help message and exit
--template-path		FILE_NAME	The path to the Terraform plan file (JSON).
--region	Yes	REGION	The destination region the resources will be deployed to.
--profile		PROFILE	The named profile to use for AWS API calls.
--enable-logging			Enables log output to stdout
--ignore-finding		FINDING_CODE, RESOURCE_NAME, RESOURCE_NAME.FINDING_CODE	Allow validation failures to be ignored. Specify as a comma separated list of findings to be ignored. Can be individual finding codes (e.g. "PASS_ROLE_WITH_STAR_IN_RESOURCE"), a specific resource name (e.g. "MyResource"), or a combination of both separated by a period.(e.g. "MyResource.PASS_ROLE_WITH_STAR_IN_RESOURCE"). Names of finding codes may change in IAM Access Analyzer over time.
--reference-policy	Yes	FILE_PATH.json	A JSON formatted file that specifies the path to the reference policy that is used for a permissions comparison.
--reference-policy-type	Yes	IDENTITY or RESOURCE	The policy type associated with the IAM policy under analysis and the reference policy.
--treat-findings-as-non-blocking			When not specified, the tool detects any findings, it will exit with a non-zero exit code. When specified, the tool exits with an exit code of 0.
--exclude-resource-types		aws_resource_type, aws_resource_type	List of comma-separated resource types. Resource types should be the same as terraform template resource names such as aws_iam_group_policy, aws_iam_role
--config	Yes	FILE_NAME1, FILE_NAME2, ...	A list of config files for running this script

check-access-not-granted

tf-policy-validator check-access-not-granted --config iam_check/config/default.yaml --template-path iam_check/test/test_policy_accessanalyzer.json --region us-west-2 --actions lambda:invokeFunction

Parses IAM identity-based and resource-based policies from AWS Terraform templates. Then runs the policies through IAM Access Analyzer for a custom check against a list of IAM actions and/or resource ARNs. If both actions and resources are provided, a custom check will be run to determine whether access is granted to allow the specified actions on the specified resources. Returns the findings from the custom check in JSON format. Exits with a non-zero error code if any findings categorized as blocking, based on access granted to at least one of the listed IAM actions and/or resources, are found in your template. Exits with an error code of zero if all findings are non-blocking or there are no findings.

Arguments	Required	Options	Description
--help			show this help message and exit
--template-path		FILE_NAME	The path to the Terraform plan file (JSON).
--region	Yes	REGION	The destination region the resources will be deployed to.
--profile		PROFILE	The named profile to use for AWS API calls.
--enable-logging			Enables log output to stdout
--ignore-finding		FINDING_CODE,RESOURCE_NAME,RESOURCE_NAME.FINDING_CODE	Allow validation failures to be ignored. Specify as a comma separated list of findings to be ignored. Can be individual finding codes (e.g. "PASS_ROLE_WITH_STAR_IN_RESOURCE"), a specific resource name (e.g. "MyResource"), or a combination of both separated by a period.(e.g. "MyResource.PASS_ROLE_WITH_STAR_IN_RESOURCE"). Names of finding codes may change in IAM Access Analyzer over time.
--actions	At least one of actions or resources is required.	ACTION,ACTION,ACTION	List of comma-separated actions.
--resources	At least one of actions or resources is required.	RESOURCE,RESOURCE,RESOURCE	List of comma-separated resource ARNs, maximum 100 resource ARNs.
--treat-findings-as-non-blocking			When not specified, the tool detects any findings, it will exit with a non-zero exit code. When specified, the tool exits with an exit code of 0.
--exclude-resource-types		aws_resource_type, aws_resource_type	List of comma-separated resource types. Resource types should be the same as terraform template resource names such as aws_iam_group_policy, aws_iam_role
--config	Yes	FILE_NAME1, FILE_NAME2, ...	A list of config files for running this script

check-no-public-access

tf-policy-validator check-no-public-access --config iam_check/config/default.yaml --template-path iam_check/test/test_policy_accessanalyzer.json --region us-west-2

Parses resource-based policies from Terraform templates. Then runs the policies through IAM Access Analyzer for a custom check for public access to resources. Returns the findings from the custom check in JSON format. Exits with a non-zero error code if any findings categorized as blocking, based on whether public access is granted to at least one of the resources, are found in your template. Exits with an error code of zero if all findings are non-blocking or there are no findings.

Arguments	Required	Options	Description
--help			show this help message and exit
--template-path		FILE_NAME	The path to the Terraform plan file (JSON).
--region	Yes	REGION	The destination region the resources will be deployed to.
--profile		PROFILE	The named profile to use for AWS API calls.
--enable-logging			Enables log output to stdout
--ignore-finding		FINDING_CODE, RESOURCE_NAME, RESOURCE_NAME.FINDING_CODE	Allow validation failures to be ignored. Specify as a comma separated list of findings to be ignored. Can be individual finding codes (e.g. "PASS_ROLE_WITH_STAR_IN_RESOURCE"), a specific resource name (e.g. "MyResource"), or a combination of both separated by a period.(e.g. "MyResource.PASS_ROLE_WITH_STAR_IN_RESOURCE"). Names of finding codes may change in IAM Access Analyzer over time.
--treat-findings-as-non-blocking			When not specified, the tool detects any findings, it will exit with a non-zero exit code. When specified, the tool exits with an exit code of 0.
--exclude-resource-types		aws_resource_type, aws_resource_type	List of comma-separated resource types. Resource types should be the same as terraform template resource names such as aws_iam_group_policy, aws_iam_role
--config	Yes	FILE_NAME1, FILE_NAME2, ...	A list of config files for running this script

Resource-based policies that can be checked with check-no-public-access are limited to the resource types currently supported by IAM Policy Validator for Terraform. The following resource types are supported:

• AWS::EFS::FileSystem
• AWS::OpenSearchService::Domain
• AWS::KMS::Key
• AWS::S3::Bucket
• AWS::S3::AccessPoint
• AWS::S3::Glacier
• AWS::S3Outposts::Bucket
• AWS::SecretsManager::Secret
• AWS::SNS::Topic
• AWS::SQS::Queue
• Role trust policies (AWS::IAM::AssumeRolePolicyDocument)

Example to check Terraform template

$ cd iam_check/test/
$ terraform init
$ terraform plan -out tf.plan ## generate terraform plan file
$ terraform show -json -no-color tf.plan > tf.json ## convert plan files to machine-readable JSON files. For TF 0.12 and prior, use command `terraform show tf.plan > tf.out`
$ cd ../..
$ tf-policy-validator --config iam_check/config/default.yaml --template-path iam_check/test/tf.json --region us-east-1 --treat-finding-type-as-blocking ERROR # For TF 0.12 and prior, replace tf.json with tf.out
$ tf-policy-validator check-no-new-access --config iam_check/config/default.yaml --template-path iam_check/test/test_policy_accessanalyzer.json --region us-west-2 --reference-policy-type identity --reference-policy iam_check/test/test_policy.json
$ tf-policy-validator check-access-not-granted --config iam_check/config/default.yaml --template-path iam_check/test/test_policy_accessanalyzer.json --region us-west-2 --actions lambda:invokeFunction
$ tf-policy-validator check-no-public-access --config iam_check/config/default.yaml --template-path iam_check/test/test_policy_accessanalyzer.json --region us-west-2

More examples can be found here.

Limitations

1. Does not support Terraform computed resources. For example, the tool will report no IAM policy found for the following Terraform template. The policy json string is a computed resource. The plan output doesn't contain information of IAM policy document.

resource "aws_s3_bucket" "b" {
  bucket = "my-tf-test-bucket"

  tags = {
    Name        = "My bucket"
    Environment = "Dev"
  }
}

resource "aws_iam_policy" "policy" {
  name        = "test-policy"
  description = "A test policy"

  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = [
          "s3:GetObject",
        ]
        Effect   = "Allow"
        Resource = "${aws_s3_bucket.b.id}"
      }
    ]
  })
}

Frequently Asked Questions

How to run unit tests

$ python3 -m pip install pipenv
$ pipenv install --dev
$ pipenv shell
$ cd iam_check
$ python3 -m pytest

Contributors

Contributors