tf-policy-validator 0.0.2

A command line tool that validates AWS IAM Policies in a Terraform template against AWS IAM best practices

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.

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"
            ],
            "Resource": "*"
        }
    ]
}

Action Name	Justificiation
access-analyzer:ValidatePolicy	Called for each policy to validate against IAM policy best practices.

Basic usage

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

Avaliable commands

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

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

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