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4.13 Ensure route table changes are monitored

Information

Real-time monitoring of API calls can be achieved by directing CloudTrail Logs to CloudWatch Logs, or an external Security information and event management (SIEM) environment, and establishing corresponding metric filters and alarms. Routing tables are used to route network traffic between subnets and to network gateways. It is recommended that a metric filter and alarm be established for changes to route tables.

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 changes to route tables will help ensure that all VPC traffic flows through an expected path and prevent any accidental or intentional modifications that may lead to uncontrolled network traffic. An alarm should be triggered every time an AWS API call is performed to create, replace, delete, or disassociate a Route Table.

NOTE: Nessus has not performed this check. Please review the benchmark to ensure target compliance.

Solution

If you are using CloudTrails and CloudWatch, perform the following to setup the metric filter, alarm, SNS topic, and subscription:

Create a metric filter based on filter pattern provided which checks for route table 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 '<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 monitoring alarms.

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>

See Also

https://workbench.cisecurity.org/benchmarks/10599

Item Details

Category: AUDIT AND ACCOUNTABILITY

References: 800-53|AU-6, 800-53|AU-6(1), 800-53|AU-7(1), CCE|CCE-79198-8, CSCv7|6.2, CSCv7|11.3

Plugin: amazon_aws

Control ID: 4a73ef86992de61eab32b7b3fd06207fad7ce29d9dbb92838d852e3c67603d19