Adding a Config Rule to test for External Account in S3 bucket policies

python-rdklib/S3_POLICY_OUTSIDE_ACCESS/S3_POLICY_OUTSIDE_ACCESS/Lambda layers/config_lambda_layer.py/config_lambda_layer.py

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+# Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+
+import json
+import sys
+import datetime
+import boto3
+import botocore
+
+try:
+    import liblogging
+except ImportError:
+    pass
+
+# Set to True to get the lambda to assume the Role attached on the Config Service (useful for cross-account).
+ASSUME_ROLE_MODE = False
+
+# Other parameters (no change needed)
+CONFIG_ROLE_TIMEOUT_SECONDS = 900
+DEFAULT_RESOURCE_TYPE = 'AWS::::Account'
+
+config = boto3.client('config')
+
+
+def evaluate_parameters(rule_parameters):
+    kmskeyid_list = {}
+    if "KmsKeyId" in rule_parameters:
+        kmskeyid_list = [kmskeyid.strip() for kmskeyid in rule_parameters['KmsKeyId'].split(',')]
+        kmskeyid_list = list(filter(None, kmskeyid_list))
+
+        for arn in kmskeyid_list:
+            if not arn.startswith("arn:aws:kms:"):
+                raise ValueError(
+                    'Invalid value for the parameter "KmsKeyId", expected valid ARN(s) of Kms Key'
+                )
+    return kmskeyid_list
+
+####################
+# Helper Functions #
+####################
+
+# Build an error to be displayed in the logs when the parameter is invalid.
+def build_parameters_value_error_response(ex):
+    """Return an error dictionary when the evaluate_parameters() raises a ValueError.
+    Keyword arguments:
+    ex -- Exception text
+    """
+    return  build_error_response(internal_error_message="Parameter value is invalid",
+                                 internal_error_details="An ValueError was raised during the validation of the Parameter value",
+                                 customer_error_code="InvalidParameterValueException",
+                                 customer_error_message=str(ex))
+
+# This gets the client after assuming the Config service role
+# either in the same AWS account or cross-account.
+def get_client(service, event):
+    """Return the service boto client. It should be used instead of directly calling the client.
+    Keyword arguments:
+    service -- the service name used for calling the boto.client()
+    event -- the event variable given in the lambda handler
+    """
+    if not ASSUME_ROLE_MODE:
+        return boto3.client(service)
+    credentials = get_assume_role_credentials(event["executionRoleArn"])
+    return boto3.client(service, aws_access_key_id=credentials['AccessKeyId'],
+                        aws_secret_access_key=credentials['SecretAccessKey'],
+                        aws_session_token=credentials['SessionToken']
+                       )
+
+# This generate an evaluation for config
+def build_evaluation(resource_id, compliance_type, event, resource_type=DEFAULT_RESOURCE_TYPE, annotation=None):
+    """Form an evaluation as a dictionary. Usually suited to report on scheduled rules.
+    Keyword arguments:
+    resource_id -- the unique id of the resource to report
+    compliance_type -- either COMPLIANT, NON_COMPLIANT or NOT_APPLICABLE
+    event -- the event variable given in the lambda handler
+    resource_type -- the CloudFormation resource type (or AWS::::Account) to report on the rule (default DEFAULT_RESOURCE_TYPE)
+    annotation -- an annotation to be added to the evaluation (default None)
+    """
+    eval_cc = {}
+    if annotation:
+        eval_cc['Annotation'] = annotation
+    eval_cc['ComplianceResourceType'] = resource_type
+    eval_cc['ComplianceResourceId'] = resource_id
+    eval_cc['ComplianceType'] = compliance_type
+    eval_cc['OrderingTimestamp'] = str(json.loads(event['invokingEvent'])['notificationCreationTime'])
+    return eval_cc
+
+def build_evaluation_from_config_item(configuration_item, compliance_type, annotation=None):
+    """Form an evaluation as a dictionary. Usually suited to report on configuration change rules.
+    Keyword arguments:
+    configuration_item -- the configurationItem dictionary in the invokingEvent
+    compliance_type -- either COMPLIANT, NON_COMPLIANT or NOT_APPLICABLE
+    annotation -- an annotation to be added to the evaluation (default None)
+    """
+    eval_ci = {}
+    if annotation:
+        eval_ci['Annotation'] = annotation
+    eval_ci['ComplianceResourceType'] = configuration_item['resourceType']
+    eval_ci['ComplianceResourceId'] = configuration_item['resourceId']
+    eval_ci['ComplianceType'] = compliance_type
+    eval_ci['OrderingTimestamp'] = configuration_item['configurationItemCaptureTime']
+    return eval_ci
+
+####################
+# Boilerplate Code #
+####################
+
+# Helper function used to validate input
+def check_defined(reference, reference_name):
+    if not reference:
+        raise Exception('Error: ', reference_name, 'is not defined')
+    return reference
+
+# Check whether the message is OversizedConfigurationItemChangeNotification or not
+def is_oversized_changed_notification(message_type):
+    check_defined(message_type, 'messageType')
+    return message_type == 'OversizedConfigurationItemChangeNotification'
+
+# Check whether the message is a ScheduledNotification or not.
+def is_scheduled_notification(message_type):
+    check_defined(message_type, 'messageType')
+    return message_type == 'ScheduledNotification'
+
+# Get configurationItem using getResourceConfigHistory API
+# in case of OversizedConfigurationItemChangeNotification
+def get_configuration(resource_type, resource_id, configuration_capture_time):
+    result = config.get_resource_config_history(
+        resourceType=resource_type,
+        resourceId=resource_id,
+        laterTime=configuration_capture_time,
+        limit=1)
+    configuration_item = result['configurationItems'][0]
+    return convert_api_configuration(configuration_item)
+
+# Convert from the API model to the original invocation model
+def convert_api_configuration(configuration_item):
+    for k, v in configuration_item.items():
+        if isinstance(v, datetime.datetime):
+            configuration_item[k] = str(v)
+    configuration_item['awsAccountId'] = configuration_item['accountId']
+    configuration_item['ARN'] = configuration_item['arn']
+    configuration_item['configurationStateMd5Hash'] = configuration_item['configurationItemMD5Hash']
+    configuration_item['configurationItemVersion'] = configuration_item['version']
+    configuration_item['configuration'] = json.loads(configuration_item['configuration'])
+    if 'relationships' in configuration_item:
+        for i in range(len(configuration_item['relationships'])):
+            configuration_item['relationships'][i]['name'] = configuration_item['relationships'][i]['relationshipName']
+    return configuration_item
+
+# Based on the type of message get the configuration item
+# either from configurationItem in the invoking event
+# or using the getResourceConfigHistiry API in getConfiguration function.
+def get_configuration_item(invoking_event):
+    check_defined(invoking_event, 'invokingEvent')
+    if is_oversized_changed_notification(invoking_event['messageType']):
+        configuration_item_summary = check_defined(invoking_event['configuration_item_summary'], 'configurationItemSummary')
+        return get_configuration(configuration_item_summary['resourceType'], configuration_item_summary['resourceId'], configuration_item_summary['configurationItemCaptureTime'])
+    if is_scheduled_notification(invoking_event['messageType']):
+        return None
+    return check_defined(invoking_event['configurationItem'], 'configurationItem')
+
+# Check whether the resource has been deleted. If it has, then the evaluation is unnecessary.
+def is_applicable(configuration_item, event):
+    try:
+        check_defined(configuration_item, 'configurationItem')
+        check_defined(event, 'event')
+    except:
+        return True
+    status = configuration_item['configurationItemStatus']
+    event_left_scope = event['eventLeftScope']
+    if status == 'ResourceDeleted':
+        print("Resource Deleted, setting Compliance Status to NOT_APPLICABLE.")
+    return status in ('OK', 'ResourceDiscovered') and not event_left_scope
+
+def get_assume_role_credentials(role_arn):
+    sts_client = boto3.client('sts')
+    try:
+        assume_role_response = sts_client.assume_role(RoleArn=role_arn,
+                                                      RoleSessionName="configLambdaExecution",
+                                                      DurationSeconds=CONFIG_ROLE_TIMEOUT_SECONDS)
+        if 'liblogging' in sys.modules:
+            liblogging.logSession(role_arn, assume_role_response)
+        return assume_role_response['Credentials']
+    except botocore.exceptions.ClientError as ex:
+        # Scrub error message for any internal account info leaks
+        print(str(ex))
+        if 'AccessDenied' in ex.response['Error']['Code']:
+            ex.response['Error']['Message'] = "AWS Config does not have permission to assume the IAM role."
+        else:
+            ex.response['Error']['Message'] = "InternalError"
+            ex.response['Error']['Code'] = "InternalError"
+        raise ex
+
+# This removes older evaluation (usually useful for periodic rule not reporting on AWS::::Account).
+def clean_up_old_evaluations(latest_evaluations, event):
+
+    cleaned_evaluations = []
+    old_eval = config.get_compliance_details_by_config_rule(
+        ConfigRuleName=event['configRuleName'],
+        ComplianceTypes=['COMPLIANT', 'NON_COMPLIANT'],
+        Limit=100)
+
+    old_eval_list = []
+
+    while True:
+        for old_result in old_eval['EvaluationResults']:
+            old_eval_list.append(old_result)
+        if 'NextToken' in old_eval:
+            next_token = old_eval['NextToken']
+            old_eval = config.get_compliance_details_by_config_rule(
+                ConfigRuleName=event['configRuleName'],
+                ComplianceTypes=['COMPLIANT', 'NON_COMPLIANT'],
+                Limit=100,
+                NextToken=next_token)
+        else:
+            break
+
+    for old_eval in old_eval_list:
+        old_resource_id = old_eval['EvaluationResultIdentifier']['EvaluationResultQualifier']['ResourceId']
+        newer_founded = False
+        for latest_eval in latest_evaluations:
+            if old_resource_id == latest_eval['ComplianceResourceId']:
+                newer_founded = True
+        if not newer_founded:
+            cleaned_evaluations.append(build_evaluation(old_resource_id, "NOT_APPLICABLE", event))
+
+    return cleaned_evaluations + latest_evaluations
+
+
+def is_internal_error(exception):
+    return ((not isinstance(exception, botocore.exceptions.ClientError)) or exception.response['Error']['Code'].startswith('5')
+            or 'InternalError' in exception.response['Error']['Code'] or 'ServiceError' in exception.response['Error']['Code'])
+
+def build_internal_error_response(internal_error_message, internal_error_details=None):
+    return build_error_response(internal_error_message, internal_error_details, 'InternalError', 'InternalError')
+
+def build_error_response(internal_error_message, internal_error_details=None, customer_error_code=None, customer_error_message=None):
+    error_response = {
+        'internalErrorMessage': internal_error_message,
+        'internalErrorDetails': internal_error_details,
+        'customerErrorMessage': customer_error_message,
+        'customerErrorCode': customer_error_code
+    }
+    print(error_response)
+    return error_response

python-rdklib/S3_POLICY_OUTSIDE_ACCESS/S3_POLICY_OUTSIDE_ACCESS/Lambda layers/lambda layer stack.yaml/lambda layer.yaml

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+# Copyright 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+Transform: AWS::Serverless-2016-10-31
+
+Description: 'This template creates AWS Config lambda Layer'
+
+Resources:
+  ConfigLambdaLayer:
+    Type: AWS::Serverless::LayerVersion
+    Properties:
+      LayerName: Config-Lambda-Layer
+      Description: Lambda Layer for config rules boilerplate code
+      CompatibleRuntimes:
+        - python3.6
+        - python3.7
+        - python3.8
+      ContentUri: 's3://custom-config-lambda-2/python.zip'