Control: 4.13 Ensure a log metric filter and alarm exist for route table changes

Description

Real-time monitoring of API calls can be achieved by directing CloudTrail Logs to CloudWatch Logs and establishing corresponding metric filters and alarms. Network gateways are required to send/receive traffic to a destination outside of a VPC. It is recommended that a metric filter and alarm be established for changes to network gateways.

Monitoring changes to network gateways will help ensure that all ingress/egress traffic traverses the VPC border via a controlled path.

Remediation

The steps to remediate this issue include setting up an Amazon SNS topic, a metric filter, and an alarm for the metric filter.

From Console

To create SNS topic

Open the Amazon SNS console at SNS.
Create an Amazon SNS topic that receives all CIS alarms. Create at least one subscriber to the topic. You can follow steps here
Set up an active CloudTrail that applies to all Regions. To do so, follow the remediation steps in CIS 3.1 – Ensure CloudTrail is enabled in all Regions.
Make a note of the associated log group name.

To create a metric filter and alarm

Open the CloudWatch console at CloudWatch.
In the navigation pane, choose Log groups.
Select the check box for the log group that you made a note of in the previous step (4).
From Actions, choose Create Metric Filter.

Under Define pattern, do the following:

Copy the following pattern and then paste it into the Filter Pattern field.

{ ($.eventName = CreateRoute) || ($.eventName = CreateRouteTable) || ($.eventName = ReplaceRoute) || ($.eventName = ReplaceRouteTableAssociation) || ($.eventName = DeleteRouteTable) || ($.eventName = DeleteRoute) || ($.eventName = DisassociateRouteTable) }"

Choose Next.

Under Assign metric, do the following:
- In Filter name, enter a name for your metric filter.
- For Metric namespace, enter CISBenchmark. You can use the same namespace for all of your CIS log metric filters.
- For Metric name, enter a name for the metric.
- The name of the metric is required to create the alarm.
- For Metric value, enter 1.
- Choose Next.
Under Review and create, review the details and choose Create metric filter.
Choose the Metric filters tab, select the metric filter that you just created.
To choose the metric filter, select the check box at the upper right.
Choose Create Alarm.
Follow the steps provided in Create an alarm
Under Configure actions, do the following:
- Under Alarm state trigger, choose In alarm.
- Under Select an SNS topic, choose Select an existing SNS topic.
- For Send a notification to, enter the name of the SNS topic that you created in the previous procedure.
- Choose Next.
Under Add name and description, enter a Name and Description for the alarm. For example, CIS4.13-[SmallDescription]. Then choose Next.
Under Preview and create, review the alarm configuration. Choose Create alarm.

From Command Line

Perform the following to setup the metric filter, alarm, SNS topic, and subscription

Create a metric filter based on filter pattern provided and CloudWatch log group.

aws logs put-metric-filter --log-group-name <cloudtrail_log_group_name> --filter-name `<route_table_changes_metric>` --metric-transformations metricName= `<route_table_changes_metric>`,metricNamespace='CISBenchmark',metricValue=1 --filter-pattern '{($.eventName = CreateRoute) || ($.eventName = CreateRouteTable) || ($.eventName = ReplaceRoute) || ($.eventName = ReplaceRouteTableAssociation) || ($.eventName = DeleteRouteTable) || ($.eventName = DeleteRoute) || ($.eventName = DisassociateRouteTable) }'

Note: You can choose your own metricName and metricNamespace strings. Using the same metricNamespace for all Foundations Benchmark metrics will group them together.

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.

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.

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 `<route_table_changes_alarm>` --metric-name `<route_table_changes_metric>` --statistic Sum --period 300 --threshold 1 --comparison-operator GreaterThanOrEqualToThreshold --evaluation-periods 1 --namespace 'CISBenchmark' --alarm-actions <sns_topic_arn>

Usage

Run the control in your terminal:

powerpipe control run aws_compliance.control.cis_v150_4_13

Snapshot and share results via Turbot Pipes:

powerpipe login
powerpipe control run aws_compliance.control.cis_v150_4_13 --share

SQL

This control uses a named query:

with trails as (
  select
    trail.account_id,
    trail.name as trail_name,
    trail.is_logging,
    split_part(trail.log_group_arn, ':', 7) as log_group_name
  from
    aws_cloudtrail_trail as trail,
    jsonb_array_elements(trail.event_selectors) as se
  where
    trail.is_multi_region_trail is true
    and trail.is_logging
    and se ->> 'ReadWriteType' = 'All'
    and trail.log_group_arn is not null
  order by
    trail_name
),
alarms as (
  select
    metric_name,
    action_arn as topic_arn
  from
    aws_cloudwatch_alarm,
    jsonb_array_elements_text(aws_cloudwatch_alarm.alarm_actions) as action_arn
  order by
    metric_name
),
topic_subscriptions as (
  select
    subscription_arn,
    topic_arn
  from
    aws_sns_topic_subscription
  order by
    subscription_arn
),
metric_filters as (
  select
    filter.name as filter_name,
    filter_pattern,
    log_group_name,
    metric_transformation_name
  from
    aws_cloudwatch_log_metric_filter as filter
  where
    filter.filter_pattern ~ '\s*\$\.eventName\s*=\s*CreateRoute.+\$\.eventName\s*=\s*CreateRouteTable.+\$\.eventName\s*=\s*ReplaceRoute.+\$\.eventName\s*=\s*ReplaceRouteTableAssociation.+\$\.eventName\s*=\s*DeleteRouteTable.+\$\.eventName\s*=\s*DeleteRoute.+\$\.eventName\s*=\s*DisassociateRouteTable'
  order by
    filter_name
),
filter_data as (
  select
    t.account_id,
    t.trail_name,
    f.filter_name
  from
    trails as t
  join
    metric_filters as f on f.log_group_name = t.log_group_name
  join
    alarms as alarm on alarm.metric_name = f.metric_transformation_name
  join
    topic_subscriptions as subscription on subscription.topic_arn = alarm.topic_arn
)
select
  distinct 'arn:' || a.partition || ':::' || a.account_id as resource,
  case
    when f.trail_name is null then 'alarm'
    else 'ok'
  end as status,
  case
    when f.trail_name is null then 'No log metric filter and alarm exist for route table changes.'
    else filter_name || ' forwards events for route table changes.'
  end as reason
  , a.account_id
from
  aws_account as a
  left join filter_data as f on a.account_id = f.account_id;