Skip to main content

lacework-global-86

4.11 Ensure a log metric filter and alarm exist for changes to Network Access Control Lists (NACL) (Automated)​

Profile Applicability​

• Level 2

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 that a metric filter and alarm be established for changes made to NACLs.

Rationale​

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

Audit​

Perform the following to ensure that there is at least one active multi-region CloudTrail with prescribed metric filters and alarms configured:

  1. Identify the log group name configured for use with active multi-region CloudTrail:

  • List all CloudTrails: aws cloudtrail describe-trails

  • Identify Multi region CloudTrails: Trails with "IsMultiRegionTrail" set to true

  • From value associated with CloudWatchLogsLogGroupArn note <cloudtrail_log_group_name>

Example: for CloudWatchLogsLogGroupArn that looks like arn:aws:logs:<region>:<aws_account_number>:log-group:NewGroup:*, <cloudtrail_log_group_name> would be NewGroup

  • Ensure Identified Multi region CloudTrail is active

aws cloudtrail get-trail-status --name <Name of a Multi-region CloudTrail>

ensure IsLogging is set to TRUE

  • Ensure identified Multi-region CloudTrail captures all Management Events

aws cloudtrail get-event-selectors --trail-name <trailname shown in describe-trails>

Ensure there is at least one Event Selector for a Trail with IncludeManagementEvents set to true and ReadWriteType set to All

  1. Get a list of all associated metric filters for this <cloudtrail_log_group_name>:
aws logs describe-metric-filters --log-group-name "<cloudtrail_log_group_name>"
  1. Ensure the output from the above command contains the following:
"filterPattern": "{ ($.eventName = CreateNetworkAcl) || ($.eventName = CreateNetworkAclEntry) || ($.eventName = DeleteNetworkAcl) || ($.eventName = DeleteNetworkAclEntry) || ($.eventName = ReplaceNetworkAclEntry) || ($.eventName = ReplaceNetworkAclAssociation) }"

  1. Note the <nacl_changes_metric> value associated with the filterPattern found in step 3.

  2. Get a list of CloudWatch alarms and filter on the <nacl_changes_metric> captured in step 4.

aws cloudwatch describe-alarms --query 'MetricAlarms[?MetricName== `<nacl_changes_metric>`]'

  1. Note the AlarmActions value - this will provide the SNS topic ARN value.

  2. Ensure there is at least one active subscriber to the SNS topic

aws sns list-subscriptions-by-topic --topic-arn <sns_topic_arn>

at least one subscription should have "SubscriptionArn" with valid aws ARN.

Example of valid "SubscriptionArn": "arn:aws:sns:<region>:<aws_account_number>:<SnsTopicName>:<SubscriptionID>"

Remediation​

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

  1. Create a metric filter based on filter pattern provided which checks for NACL 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 `<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.

  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 monitoring alarms.

  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 'CISBenchmark' --alarm-actions <sns_topic_arn>

References​

CCE-79196-2
https://docs.aws.amazon.com/awscloudtrail/latest/userguide/receive-cloudtrail-log-files-from-multiple-regions.html
https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.html
https://docs.aws.amazon.com/sns/latest/dg/SubscribeTopic.html

Additional Information​

Configuring log metric filter and alarm on Multi-region (global) CloudTrail

  • ensures that activities from all regions (used as well as unused) are monitored
  • ensures that activities on all supported global services are monitored
  • ensures that all management events across all regions are monitored