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Allowlisting

Sometimes you may find resources that are intentionally configured in a certain way that may be a bad practice but it is all right with it, for example an AWS S3 Bucket open to the internet hosting a web site, or an AWS Security Group with an open port needed in your use case.

Allowlist option works along with other options and adds a WARNING instead of INFO, PASS or FAIL to any output format.

You can use -w/--allowlist-file with the path of your allowlist yaml file, but first, let's review the syntax.

Allowlist Yaml File Syntax

### Account, Check and/or Region can be * to apply for all the cases.
### Resources and tags are lists that can have either Regex or Keywords.
### Tags is an optional list that matches on tuples of 'key=value' and are "ANDed" together.
### Use an alternation Regex to match one of multiple tags with "ORed" logic.
### For each check you can except Accounts, Regions, Resources and/or Tags.
###########################  ALLOWLIST EXAMPLE  ###########################
Allowlist:
  Accounts:
    "123456789012":
      Checks:
        "iam_user_hardware_mfa_enabled":
          Regions:
            - "us-east-1"
          Resources:
            - "user-1"           # Will ignore user-1 in check iam_user_hardware_mfa_enabled
            - "user-2"           # Will ignore user-2 in check iam_user_hardware_mfa_enabled
        "ec2_*":
          Regions:
            - "*"
          Resources:
            - "*"                 # Will ignore every EC2 check in every account and region
        "*":
          Regions:
            - "*"
          Resources:
            - "test"
          Tags:
            - "test=test"         # Will ignore every resource containing the string "test" and the tags 'test=test' and
            - "project=test|project=stage" # either of ('project=test' OR project=stage) in account 123456789012 and every region

    "*":
      Checks:
        "s3_bucket_object_versioning":
          Regions:
            - "eu-west-1"
            - "us-east-1"
          Resources:
            - "ci-logs"           # Will ignore bucket "ci-logs" AND ALSO bucket "ci-logs-replica" in specified check and regions
            - "logs"              # Will ignore EVERY BUCKET containing the string "logs" in specified check and regions
            - ".+-logs"           # Will ignore all buckets containing the terms ci-logs, qa-logs, etc. in specified check and regions
        "ecs_task_definitions_no_environment_secrets":
          Regions:
            - "*"
          Resources:
            - "*"
          Exceptions:
            Accounts:
              - "0123456789012"
            Regions:
              - "eu-west-1"
              - "eu-south-2"        # Will ignore every resource in check ecs_task_definitions_no_environment_secrets except the ones in account 0123456789012 located in eu-south-2 or eu-west-1
        "*":
          Regions:
            - "*"
          Resources:
            - "*"
          Tags:
            - "environment=dev"    # Will ignore every resource containing the tag 'environment=dev' in every account and region

    "123456789012":
      Checks:
        "*":
          Regions:
            - "*"
          Resources:
            - "*"
          Exceptions:
            Resources:
              - "test"
            Tags:
              - "environment=prod"   # Will ignore every resource except in account 123456789012 except the ones containing the string "test" and tag environment=prod

Allowlist specific regions

If you want to allowlist/mute failed findings only in specific regions, create a file with the following syntax and run it with prowler aws -w allowlist.yaml:

Allowlist:
  Accounts:
  "*":
    Checks:
      "*":
        Regions:
          - "ap-southeast-1"
          - "ap-southeast-2"
        Resources:
          - "*"

Default AWS Allowlist

Prowler provides you a Default AWS Allowlist with the AWS Resources that should be allowlisted such as all resources created by AWS Control Tower when setting up a landing zone. You can execute Prowler with this allowlist using the following command:

prowler aws --allowlist prowler/config/aws_allowlist.yaml

Supported Allowlist Locations

The allowlisting flag supports the following locations:

Local file

You will need to pass the local path where your Allowlist YAML file is located:

prowler <provider> -w allowlist.yaml

AWS S3 URI

You will need to pass the S3 URI where your Allowlist YAML file was uploaded to your bucket:

prowler aws -w s3://<bucket>/<prefix>/allowlist.yaml

Make sure that the used AWS credentials have s3:GetObject permissions in the S3 path where the allowlist file is located.

AWS DynamoDB Table ARN

You will need to pass the DynamoDB Allowlist Table ARN:

prowler aws -w arn:aws:dynamodb:<region_name>:<account_id>:table/<table_name>
  1. The DynamoDB Table must have the following String keys:

  2. The Allowlist Table must have the following columns:

    • Accounts (String): This field can contain either an Account ID or an * (which applies to all the accounts that use this table as an allowlist).
    • Checks (String): This field can contain either a Prowler Check Name or an * (which applies to all the scanned checks).
    • Regions (List): This field contains a list of regions where this allowlist rule is applied (it can also contains an * to apply all scanned regions).
    • Resources (List): This field contains a list of regex expressions that applies to the resources that are wanted to be allowlisted.
    • Tags (List): -Optional- This field contains a list of tuples in the form of 'key=value' that applies to the resources tags that are wanted to be allowlisted.
    • Exceptions (Map): -Optional- This field contains a map of lists of accounts/regions/resources/tags that are wanted to be excepted in the allowlist.

The following example will allowlist all resources in all accounts for the EC2 checks in the regions eu-west-1 and us-east-1 with the tags environment=dev and environment=prod, except the resources containing the string test in the account 012345678912 and region eu-west-1 with the tag environment=prod:

Make sure that the used AWS credentials have dynamodb:PartiQLSelect permissions in the table.

AWS Lambda ARN

You will need to pass the AWS Lambda Function ARN:

prowler aws -w arn:aws:lambda:REGION:ACCOUNT_ID:function:FUNCTION_NAME

Make sure that the credentials that Prowler uses can invoke the Lambda Function:

- PolicyName: GetAllowList
  PolicyDocument:
    Version: '2012-10-17'
    Statement:
      - Action: 'lambda:InvokeFunction'
        Effect: Allow
        Resource: arn:aws:lambda:REGION:ACCOUNT_ID:function:FUNCTION_NAME

The Lambda Function can then generate an Allowlist dynamically. Here is the code an example Python Lambda Function that generates an Allowlist:

def handler(event, context):
  checks = {}
  checks["vpc_flow_logs_enabled"] = { "Regions": [ "*" ], "Resources": [ "" ], Optional("Tags"): [ "key:value" ] }

  al = { "Allowlist": { "Accounts": { "*": { "Checks": checks } } } }
  return al