Description

Real-time monitoring of API calls can be achieved by directing CloudTrail logs to CloudWatch logs 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 to set up a metric filter and alarm for detecting changes made to NACLs to ensure AWS resources and services are not unintentionally exposed.

Remediation

For instructions on setting up CloudWatch metric filters and alarms for NACL changes, refer to the AWS CloudWatch Alarms for CloudTrail User Guide.

aws logs put-metric-filter --log-group-name <cloudtrail_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)}'

You can choose your own metricName and metricNamespace strings. Use the same metricNamespace for all Foundations Benchmark metrics to group them together.