Network_Gateway_Change_Log_Metric

Owned by Saumitra Das
Oct 12, 2021
2 min read

Severity: Medium

Description: Ensures Log metric filter and alarm exist for changes to network gateways.

Remediation Steps:

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

Method1: Via CLI

  1. Create a metric filter based on filter pattern provided which checks for unauthorized API calls and the <cloudtrail_log_group_name>

    • # aws logs put-metric-filter --log-group-name <cloudtrail_log_group_name> --filter-name <Name_for_metric> --metric-transformations metricName=<Name_for_metric>,metricNamespace='CISBenchmark',metricValue=1 --filter-pattern '{ ($.eventName = CreateCustomerGateway) || ($.eventName = DeleteCustomerGateway) || ($.eventName = AttachInternetGateway) || ($.eventName = CreateInternetGateway) || ($.eventName = DeleteInternetGateway) || ($.eventName = DetachInternetGateway) }'
      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 <Name_for_alarm> --metric-name <Name_for_metric> --statistic Sum --period 300 --threshold 1 --comparison-operator GreaterThanOrEqualToThreshold --evaluation-periods 1 --namespace 'CISBenchmark' --alarm-actions <sns_topic_arn>
    Note: set the period and threshold to values that fit your organization.

Method2: Via AWS Management Console

Refer to the instructions at:

https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.html#cloudwatch-alarms-for-cloudtrail-gateway-changes

Note: On the Create Alarm > Alarm Threshold page, for the Whenever: <metric name> field, setting 3 has changed from For <number of> consecutive period(s) to <number> out of <number> datapoints. This should be configured as for: 1 out of 1 datapoints.

Additionally, the Additional Settings section has been newly added in the Alarm Threshold page. In this section, in the Treat missing data as drop-down list, select missing.

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