AWS CloudFormation Stack IAM Service Role

Description

Associating IAM roles with CloudFormation stacks ensures least privilege when making changes to your account.

Query · python

def policy(resource):
    # Ignore stack sets as this setting cannot be set on those
    if resource["Name"].startswith("StackSet-"):
        return True

    return resource["RoleARN"] is not None

Analyst notes

Create a new IAM role to be assumable by the cloudformation service, and then update the current stack with the --role-arn argument.

Raw source AWS CloudFormation Stack IAM Service Role · Panther Python
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Published by panther-labs/panther-analysis ↗, licensed under Apache 2.0 ↗. Reproduced here unmodified. 
AnalysisType: policy
Filename: aws_cloudformation_stack_uses_iam_role.py
PolicyID: "AWS.CloudFormation.Stack.UsesIAMServiceRole"
DisplayName: "AWS CloudFormation Stack IAM Service Role"
Enabled: true
ResourceTypes:
  - AWS.CloudFormation.Stack
Tags:
  - AWS
  - Operations
  - Panther
Severity: Info
Description: >
  Associating IAM roles with CloudFormation stacks ensures least privilege when making
  changes to your account.
Runbook: >
  Create a new IAM role to be assumable by the cloudformation service, and then update the
  current stack with the --role-arn argument.
Reference: https://amzn.to/2HAdfny
Tests:
  - Name: IAM Service Role Attached
    ExpectedResult: true
    Resource:
      {
        "AccountId": "123456789012",
        "Region": "us-west-2",
        "ARN": "arn:aws:cloudformation:us-west-2:123456789012:stack/iam-roles/1",
        "ID": "arn:aws:cloudformation:us-west-2:123456789012:stack/iam-roles/1",
        "Name": "iam-roles",
        "Tags": {},
        "ResourceID": "arn:aws:cloudformation:us-west-2:123456789012:stack/iam-roles/1",
        "ResourceType": "AWS.CloudFormation.Stack",
        "TimeCreated": "2019-01-01T00:00:00.000Z",
        "Capabilities": ["CAPABILITY_NAMED_IAM"],
        "ChangeSetId": null,
        "DeletionTime": null,
        "Description": "IAM role stack",
        "DisableRollback": false,
        "DriftInformation":
          {
            "LastCheckTimestamp": "2019-01-01T00:00:00Z",
            "StackDriftStatus": "IN-SYNC",
          },
        "EnableTerminationProtection": null,
        "LastUpdatedTime": "2019-01-01T00:00:00Z",
        "NotificationARNs": [],
        "Outputs": null,
        "Parameters":
          [
            {
              "ParameterKey": "MaxSessionDurationSec",
              "ParameterValue": "10000",
              "ResolvedValue": null,
              "UsePreviousValue": null,
            },
            {
              "ParameterKey": "Prefix",
              "ParameterValue": "Dev",
              "ResolvedValue": null,
              "UsePreviousValue": null,
            },
          ],
        "ParentId": null,
        "RoleARN": "arn:aws:iam::123456789012:role/CFNServiceRole",
        "RollbackConfiguration":
          { "MonitoringTimeInMinutes": null, "RollbackTriggers": [] },
        "RootId": null,
        "StackId": "arn:aws:cloudformation:us-west-2:123456789012:stack/iam-roles/1",
        "StackStatus": "UPDATE_COMPLETE",
        "StackStatusReason": null,
        "TimeoutInMinutes": null,
        "Drifts": [],
      }
  - Name: No Service Role Provided
    ExpectedResult: false
    Resource:
      {
        "AccountId": "123456789012",
        "Region": "us-west-2",
        "ARN": "arn:aws:cloudformation:us-west-2:123456789012:stack/iam-roles/1",
        "ID": "arn:aws:cloudformation:us-west-2:123456789012:stack/iam-roles/1",
        "Name": "iam-roles",
        "Tags": {},
        "ResourceID": "arn:aws:cloudformation:us-west-2:123456789012:stack/iam-roles/1",
        "ResourceType": "AWS.CloudFormation.Stack",
        "TimeCreated": "2019-01-01T17:16:30.000Z",
        "Capabilities": ["CAPABILITY_NAMED_IAM"],
        "ChangeSetId": null,
        "DeletionTime": null,
        "Description": "IAM role stack",
        "DisableRollback": false,
        "DriftInformation":
          {
            "LastCheckTimestamp": "2019-01-01T00:00:00Z",
            "StackDriftStatus": "IN-SYNC",
          },
        "EnableTerminationProtection": null,
        "LastUpdatedTime": "2019-01-01T00:00:00Z",
        "NotificationARNs": [],
        "Outputs": null,
        "Parameters":
          [
            {
              "ParameterKey": "MaxSessionDurationSec",
              "ParameterValue": "10000",
              "ResolvedValue": null,
              "UsePreviousValue": null,
            },
            {
              "ParameterKey": "Prefix",
              "ParameterValue": "Dev",
              "ResolvedValue": null,
              "UsePreviousValue": null,
            },
          ],
        "ParentId": null,
        "RoleARN": null,
        "RollbackConfiguration":
          { "MonitoringTimeInMinutes": null, "RollbackTriggers": [] },
        "RootId": null,
        "StackId": "arn:aws:cloudformation:us-west-2:123456789012:stack/iam-roles/1",
        "StackStatus": "UPDATE_COMPLETE",
        "StackStatusReason": null,
        "TimeoutInMinutes": null,
        "Drifts": [],
      }
  - Name: No Service Role Provided But Stack Is StackSet
    ExpectedResult: true
    Resource:
      {
        "AccountId": "123456789012",
        "Region": "us-west-2",
        "ARN": "arn:aws:cloudformation:us-west-2:123456789012:stack/StackSet-iam-roles/1",
        "ID": "arn:aws:cloudformation:us-west-2:123456789012:stack/StackSet-iam-roles/1",
        "Name": "StackSet-iam-roles",
        "Tags": {},
        "ResourceID": "arn:aws:cloudformation:us-west-2:123456789012:stack/StackSet-iam-roles/1",
        "ResourceType": "AWS.CloudFormation.Stack",
        "TimeCreated": "2019-01-01T00:00:00.000Z",
        "Capabilities": ["CAPABILITY_NAMED_IAM"],
        "ChangeSetId": null,
        "DeletionTime": null,
        "Description": "IAM role stack set",
        "DisableRollback": false,
        "DriftInformation":
          {
            "LastCheckTimestamp": "2019-01-01T00:00:00Z",
            "StackDriftStatus": "IN-SYNC",
          },
        "EnableTerminationProtection": null,
        "LastUpdatedTime": "2019-01-01T00:00:00Z",
        "NotificationARNs": [],
        "Outputs": null,
        "Parameters":
          [
            {
              "ParameterKey": "MaxSessionDurationSec",
              "ParameterValue": "10000",
              "ResolvedValue": null,
              "UsePreviousValue": null,
            },
            {
              "ParameterKey": "Prefix",
              "ParameterValue": "Dev",
              "ResolvedValue": null,
              "UsePreviousValue": null,
            },
          ],
        "ParentId": null,
        "RoleARN": null,
        "RollbackConfiguration":
          { "MonitoringTimeInMinutes": null, "RollbackTriggers": [] },
        "RootId": null,
        "StackStatus": "UPDATE_COMPLETE",
        "StackStatusReason": null,
        "TimeoutInMinutes": null,
        "Drifts": [],
      }


# ------ paired body: aws_cloudformation_stack_uses_iam_role.py ------

def policy(resource):
    # Ignore stack sets as this setting cannot be set on those
    if resource["Name"].startswith("StackSet-"):
        return True

    return resource["RoleARN"] is not None

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