control 'aws-foundations-cis-4.15' do
  title 'Ensure AWS Organizations changes are monitored '
  desc "Real-time monitoring of API calls can be achieved by directing CloudTrail Logs to CloudWatch
Logs, and establishing corresponding metric filters and alarms. It is recommended that a
metric filter and alarm be established for AWS Organizations changes made in the master AWS
Account. "
  desc 'rationale',
       "CloudWatch is an AWS native service that allows you to observe and monitor resources and
applications. CloudTrail Logs can also be sent to an external Security information and event
management (SIEM) environment for monitoring and alerting.

Monitoring AWS
Organizations changes can help you prevent any unwanted, accidental or intentional
modifications that may lead to unauthorized access or other security breaches. This
monitoring technique helps you to ensure that any unexpected changes performed within your
AWS Organizations can be investigated and any unwanted changes can be rolled back. "
  desc 'check',
       "If you are using CloudTrails and CloudWatch, perform the following:

1. Ensure that there
is at least one active multi-region CloudTrail with prescribed metric filters and alarms
configured:
- Identify the log group name configured for use with active multi-region
CloudTrail:
- List all CloudTrails:
```
aws cloudtrail describe-trails
```
-
Identify Multi region Cloudtrails, Trails with `\"IsMultiRegionTrail\"` set to true
- From
value associated with CloudWatchLogsLogGroupArn note <cloudtrail_log_group_name>

**Example:** for CloudWatchLogsLogGroupArn that looks like
arn:aws:logs:<region>:<aws_account_number>:log-group:NewGroup:*,
<cloudtrail_log_group_name> would be NewGroup

- Ensure Identified Multi region
CloudTrail is active:
```
aws cloudtrail get-trail-status --name <Name of a
Multi-region CloudTrail>
```
Ensure `IsLogging` is set to `TRUE`

- Ensure
identified Multi-region Cloudtrail captures all Management Events:
```
aws
cloudtrail get-event-selectors --trail-name <trailname shown in
describe-trails>
```
- Ensure there is at least one Event Selector for a Trail with
`IncludeManagementEvents` set to true and `ReadWriteType` set to `All`.

2. Get a list of
all associated metric filters for this <cloudtrail_log_group_name>:
```
aws logs
describe-metric-filters --log-group-name \"<cloudtrail_log_group_name>\"
```
3.
Ensure the output from the above command contains the following:
```
\"filterPattern\":
\"{ ($.eventSource = organizations.amazonaws.com) && (($.eventName = \"AcceptHandshake\")
|| ($.eventName = \"AttachPolicy\") || ($.eventName = \"CreateAccount\") || ($.eventName =
\"CreateOrganizationalUnit\") || ($.eventName = \"CreatePolicy\") || ($.eventName =
\"DeclineHandshake\") || ($.eventName = \"DeleteOrganization\") || ($.eventName =
\"DeleteOrganizationalUnit\") || ($.eventName = \"DeletePolicy\") || ($.eventName =
\"DetachPolicy\") || ($.eventName = \"DisablePolicyType\") || ($.eventName =
\"EnablePolicyType\") || ($.eventName = \"InviteAccountToOrganization\") || ($.eventName =
\"LeaveOrganization\") || ($.eventName = \"MoveAccount\") || ($.eventName =
\"RemoveAccountFromOrganization\") || ($.eventName = \"UpdatePolicy\") || ($.eventName =
\"UpdateOrganizationalUnit\")) }\"
```
4. Note the `<organizations_changes>` value
associated with the filterPattern found in step 3.

5. Get a list of CloudWatch alarms and
filter on the `<organizations_changes>` captured in step 4:
```
aws cloudwatch
describe-alarms --query 'MetricAlarms[?MetricName==
`<organizations_changes>`]'
```
6. Note the AlarmActions value - this will provide the
SNS topic ARN value.

7. Ensure there is at least one active subscriber to the SNS
topic:
```
aws sns list-subscriptions-by-topic --topic-arn <sns_topic_arn>

```
at least one subscription should have \"SubscriptionArn\" with valid aws
ARN.
Example of valid \"SubscriptionArn\":
```
\"arn:aws:sns:<region>:<aws_account_number>:<SnsTopicName>:<SubscriptionID>\"
``` "
  desc 'fix',
       "If you are using CloudTrails and CloudWatch, perform the following to setup the metric
filter, alarm, SNS topic, and subscription:

1. Create a metric filter based on filter
pattern provided which checks for AWS Organizations changes and the
`<cloudtrail_log_group_name>` taken from audit step 1:
```
aws logs
put-metric-filter --log-group-name <cloudtrail_log_group_name> --filter-name
`<organizations_changes>` --metric-transformations metricName=
`<organizations_changes>` ,metricNamespace='CISBenchmark',metricValue=1
--filter-pattern '{ ($.eventSource = organizations.amazonaws.com) && (($.eventName =
\"AcceptHandshake\") || ($.eventName = \"AttachPolicy\") || ($.eventName = \"CreateAccount\")
|| ($.eventName = \"CreateOrganizationalUnit\") || ($.eventName = \"CreatePolicy\") ||
($.eventName = \"DeclineHandshake\") || ($.eventName = \"DeleteOrganization\") ||
($.eventName = \"DeleteOrganizationalUnit\") || ($.eventName = \"DeletePolicy\") ||
($.eventName = \"DetachPolicy\") || ($.eventName = \"DisablePolicyType\") || ($.eventName =
\"EnablePolicyType\") || ($.eventName = \"InviteAccountToOrganization\") || ($.eventName =
\"LeaveOrganization\") || ($.eventName = \"MoveAccount\") || ($.eventName =
\"RemoveAccountFromOrganization\") || ($.eventName = \"UpdatePolicy\") || ($.eventName =
\"UpdateOrganizationalUnit\")) }'
```
**Note:** You can choose your own metricName and
metricNamespace strings. Using the same metricNamespace for all Foundations Benchmark
metrics will group them together.

2. Create an SNS topic that the alarm will
notify:
```
aws sns create-topic --name <sns_topic_name>
```
**Note:** you can
execute this command once and then re-use the same topic for all monitoring alarms.

3.
Create an SNS subscription to the topic created in step 2:
```
aws sns subscribe
--topic-arn <sns_topic_arn> --protocol <protocol_for_sns> --notification-endpoint
<sns_subscription_endpoints>
```
**Note:** you can execute this command once and then
re-use the SNS subscription for all monitoring alarms.

4. Create an alarm that is
associated with the CloudWatch Logs Metric Filter created in step 1 and an SNS topic created in
step 2:
```
aws cloudwatch put-metric-alarm --alarm-name `<organizations_changes>`
--metric-name `<organizations_changes>` --statistic Sum --period 300 --threshold 1
--comparison-operator GreaterThanOrEqualToThreshold --evaluation-periods 1
--namespace 'CISBenchmark' --alarm-actions <sns_topic_arn>
``` "
  impact 0.5
  ref 'https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.html:https://docs.aws.amazon.com/organizations/latest/userguide/orgs_security_incident-response.html'
  tag nist: %w{AU-6 AU-6(1) AU-7(1)}
  tag severity: 'medium '
  tag cis_controls: [{ '8' => ['8.11'] }]

  only_if('Inputs indicate environment should be using something other than AWS CloudTrail and AWS CloudWatch for real-time monitoring of API calls. Manual review of the monitoring system required.') {
    !input('third_party_api_monitoring_tool')
  }

  pattern = '{ ($.eventSource = organizations.amazonaws.com) && (($.eventName =\"AcceptHandshake\") || ($.eventName = \"AttachPolicy\") || ($.eventName = \"CreateAccount\") || ($.eventName = \"CreateOrganizationalUnit\") || ($.eventName = \"CreatePolicy\") || ($.eventName = \"DeclineHandshake\") || ($.eventName = \"DeleteOrganization\") || ($.eventName = \"DeleteOrganizationalUnit\") || ($.eventName = \"DeletePolicy\") || ($.eventName = \"DetachPolicy\") || ($.eventName = \"DisablePolicyType\") || ($.eventName = \"EnablePolicyType\") || ($.eventName = \"InviteAccountToOrganization\") || ($.eventName = \"LeaveOrganization\") || ($.eventName = \"MoveAccount\") || ($.eventName = \"RemoveAccountFromOrganization\") || ($.eventName = \"UpdatePolicy\") || ($.eventName = \"UpdateOrganizationalUnit\")) }'

  describe aws_cloudwatch_log_metric_filter(pattern: pattern) do
    it { should exist }
  end

  # Find the log_group_name associated with the aws_cloudwatch_log_metric_filter that has the pattern
  log_group_name = aws_cloudwatch_log_metric_filter(pattern: pattern).log_group_name

  # Find cloudtrails associated with with `log_group_name` parsed above
  associated_trails = aws_cloudtrail_trails.names.select { |x| aws_cloudtrail_trail(x).cloud_watch_logs_log_group_arn =~ /log-group:#{log_group_name}:/ }

  # Ensure log_group is associated atleast one cloudtrail
  describe "Cloudtrails associated with log-group: #{log_group_name}" do
    subject { associated_trails }
    it { should_not be_empty }
  end

  # Ensure atleast one of the associated cloudtrail meet the requirements.
  describe.one do
    associated_trails.each do |trail|
      describe aws_cloudtrail_trail(trail) do
        it { should be_multi_region_trail }
        it { should have_event_selector_mgmt_events_rw_type_all }
        it { should be_logging }
      end
    end
  end

  # Parse out `metric_name` and `metric_namespace` for the specified pattern.
  associated_metric_filter = aws_cloudwatch_log_metric_filter(pattern: pattern, log_group_name: log_group_name)
  metric_name = associated_metric_filter.metric_name
  metric_namespace = associated_metric_filter.metric_namespace

  # Ensure aws_cloudwatch_alarm for the specified pattern meets requirements.
  if associated_metric_filter.exists?
    describe aws_cloudwatch_alarm(metric_name: metric_name, metric_namespace: metric_namespace) do
      it { should exist }
      its('alarm_actions') { should_not be_empty }
    end

    aws_cloudwatch_alarm(metric_name: metric_name, metric_namespace: metric_namespace).alarm_actions.each do |sns|
      describe aws_sns_topic(sns) do
        it { should exist }
        its('confirmed_subscription_count') { should cmp >= 1 }
      end
    end
  end
end
