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Ensure Network Access Control Lists (NACL) changes are monitored

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 that a metric filter and alarm be established for changes made to NACLs. Monitoring changes to NACLs will help ensure that AWS resources and services are not unintentionally exposed.

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Risk Level: Low
Cloud Entity: CloudTrail
CloudGuard Rule ID: D9.AWS.MON.11
Covered by Spectral: Yes
Category: Management Tools

GSL LOGIC

List<CloudTrail> should have items with [hasSNSSubscriber='true' and metricFilters with [filterPattern isFilterPatternEqual('{ ($.eventName = CreateNetworkAcl) || ($.eventName = CreateNetworkAclEntry) || ($.eventName = DeleteNetworkAcl) || ($.eventName =DeleteNetworkAclEntry) || ($.eventName = ReplaceNetworkAclEntry) || ($.eventName = ReplaceNetworkAclAssociation) }')] length() > 0]

REMEDIATION

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

  1. Create a metric filter based on filter pattern relevant for this check. For More details, refer to CIS Amazon Web Services Foundations Benchmark v1.5.0: https://workbench.cisecurity.org/benchmarks/7366
  2. Create an SNS topic that the alarm will notify
  3. Create an SNS subscription to the topic created in step 2
  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

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

  1. 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 nacl_changes_metric --metric-transformations metricName= nacl_changes_metric ,metricNamespace=METRIC_NAMESPACE,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.

  1. 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.

  1. 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.

  1. 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 nacl_changes_alarm --metric-name nacl_changes_metric --statistic Sum --period 300 --threshold 1 --comparison-operator GreaterThanOrEqualToThreshold --evaluation-periods 1 --namespace NAMESPACE_VALUE --alarm-actions sns_topic_arn

References

  1. https://workbench.cisecurity.org/sections/844440/recommendations/1387901
  2. https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/US_SetupSNS.html
  3. https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.html
  4. https://docs.aws.amazon.com/sns/latest/dg/sns-create-topic.html

CloudTrail

AWS CloudTrail is a service that enables governance, compliance, operational auditing, and risk auditing of your AWS account. With CloudTrail, you can log, continuously monitor, and retain account activity related to actions across your AWS infrastructure. CloudTrail provides event history of your AWS account activity, including actions taken through the AWS Management Console, AWS SDKs, command line tools, and other AWS services. This event history simplifies security analysis, resource change tracking, and troubleshooting.

Compliance Frameworks

  • AWS CIS Foundations v. 1.0.0
  • AWS CIS Foundations v. 1.1.0
  • AWS CIS Foundations v. 1.2.0
  • AWS CIS Foundations v. 1.3.0
  • AWS CIS Foundations v. 1.4.0
  • AWS CIS Foundations v. 1.5.0
  • AWS CIS Foundations v. 2.0.0
  • AWS CSA CCM v.3.0.1
  • AWS CSA CCM v.4.0.1
  • AWS CloudGuard Best Practices
  • AWS CloudGuard SOC2 based on AICPA TSC 2017
  • AWS CloudGuard Well Architected Framework
  • AWS GDPR Readiness
  • AWS HIPAA
  • AWS HITRUST
  • AWS HITRUST v11.0.0
  • AWS ISO 27001:2013
  • AWS ISO27001:2022
  • AWS ITSG-33
  • AWS LGPD regulation
  • AWS MAS TRM Framework
  • AWS MITRE ATT&CK Framework v10
  • AWS MITRE ATT&CK Framework v11.3
  • AWS NIST 800-171
  • AWS NIST 800-53 Rev 4
  • AWS NIST 800-53 Rev 5
  • AWS NIST CSF v1.1
  • AWS PCI-DSS 3.2
  • AWS PCI-DSS 4.0
  • CloudGuard AWS All Rules Ruleset

Updated over 1 year ago