Detections
Analytics

4.11 Ensure Network Access Control List (NACL) changes are monitored

Warning! Audit Deprecated

This audit has been deprecated and will be removed in a future update.

View Next Audit Version

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.

NACLs are used as a stateless packet filter to control ingress and egress traffic for subnets within a VPC. It is recommended that a metric filter and alarm be established for any changes made to NACLs.

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 NACLs will help ensure that AWS resources and services are not unintentionally exposed.

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

Solution

If you are using CloudTrail trails and CloudWatch, perform the following steps to set up the metric filter, alarm, SNS topic, and subscription:

 -

Create a metric filter based on the provided filter pattern that checks for NACL changes and uses the <trail-log-group-name> taken from audit step 1:

aws logs put-metric-filter --log-group-name <trail-log-group-name> --filter-name <nacl-changes-metric> --metric-transformations metricName=<nacl-changes-metric>,metricNamespace='CISBenchmark',metricValue=1 --filter-pattern '{ ($.eventName = CreateNetworkAcl) || ($.eventName = CreateNetworkAclEntry) || ($.eventName = DeleteNetworkAcl) || ($.eventName = DeleteNetworkAclEntry) || ($.eventName = ReplaceNetworkAclEntry) || ($.eventName = ReplaceNetworkAclAssociation) }'

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 reuse the same topic for all monitoring alarms.

Note : Capture the TopicArn that is displayed when creating the SNS topic in step 2.

 -

Create an SNS subscription for the topic created in step 2:

aws sns subscribe --topic-arn <sns-topic-arn> --protocol <sns-protocol> --notification-endpoint <sns-subscription-endpoints>

Note : You can execute this command once and then reuse the same subscription for all monitoring alarms.

 -

Create an alarm that is associated with the CloudWatch Logs metric filter created in step 1 and the SNS topic created in step 2:

aws cloudwatch put-metric-alarm --alarm-name <nacl-changes-alarm> --metric-name <nacl-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/19631

Item Details

References: CSCv7|6.3, CSCv7|11.3

Plugin: amazon_aws

Control ID: cae538b5251a08a3b88bd6b6b47687336898c19d00f640fd1efa1ef904bceb22