CloudWatch changes to NACL alarm missing

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Metadata

Id: 0a8e8dc5-b6fc-44fc-b5a1-969ec950f9b0

Cloud Provider: AWS

Platform: Terraform

Severity: Medium

Category: Observability

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Description

This check ensures that a log metric filter and an associated CloudWatch alarm are configured to monitor changes to AWS Network Access Control Lists (NACLs). Without properly linking the metric alarm to the log metric filter—such as setting the metric_name in aws_cloudwatch_metric_alarm to the correct filter like ${aws_cloudwatch_log_metric_filter.cis_changes_nacl.id}—malicious or accidental modifications to NACLs may go undetected, increasing the risk of unauthorized network access or compromised security postures. The following example ensures the alarm triggers on relevant NACL changes and notifies security teams promptly:

resource "aws_cloudwatch_metric_alarm" "cis_changes_nacl" {
  metric_name = aws_cloudwatch_log_metric_filter.cis_changes_nacl.id
  // other relevant attributes...
}

Compliant Code Examples

provider "aws" {
  region = "us-east-2"
}

resource "aws_cloudwatch_log_group" "CIS_CloudWatch_LogsGroup" {
  name = "CIS_CloudWatch_LogsGroup"
}

resource "aws_sns_topic" "cis_alerts_sns_topic" {
  name = "cis-alerts-sns-topic"
}

resource "aws_cloudwatch_metric_alarm" "cis_changes_nacl" {
  alarm_name                = "CIS-4.11-Changes-NACL"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "1"
  metric_name               = aws_cloudwatch_log_metric_filter.cis_changes_nacl.id
  namespace                 = "CIS_Metric_Alarm_Namespace"
  period                    = "300"
  statistic                 = "Sum"
  threshold                 = "1"
  alarm_actions             = [aws_sns_topic.cis_alerts_sns_topic.arn]
  insufficient_data_actions = []
}

resource "aws_cloudwatch_log_metric_filter" "cis_changes_nacl" {
  name           = "CIS-4.11-Changes-NACL"
  pattern        = "{ ($.eventName = CreateNetworkAcl) || ($.eventName = CreateNetworkAclEntry) || ($.eventName = DeleteNetworkAcl) || ($.eventName = DeleteNetworkAclEntry) || ($.eventName = ReplaceNetworkAclEntry) || ($.eventName = ReplaceNetworkAclAssociation) }"
  log_group_name = aws_cloudwatch_log_group.CIS_CloudWatch_LogsGroup.name

  metric_transformation {
    name      = "CIS-4.11-Changes-NACL"
    namespace = "CIS_Metric_Alarm_Namespace"
    value     = "1"
  }
}

Non-Compliant Code Examples

provider "aws" {
  region = "us-east-2"
}

resource "aws_cloudwatch_log_group" "CIS_CloudWatch_LogsGroup" {
  name = "CIS_CloudWatch_LogsGroup"
}

resource "aws_sns_topic" "cis_alerts_sns_topic" {
  name = "cis-alerts-sns-topic"
}

resource "aws_cloudwatch_metric_alarm" "cis_changes_nacl" {
  alarm_name                = "CIS-4.11-Changes-NACL"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "1"
  metric_name               = aws_cloudwatch_log_metric_filter.cis_changes_nacl.id
  namespace                 = "CIS_Metric_Alarm_Namespace"
  period                    = "300"
  statistic                 = "Sum"
  threshold                 = "1"
  alarm_actions             = [aws_sns_topic.cis_alerts_sns_topic.arn]
  insufficient_data_actions = []
}

resource "aws_cloudwatch_log_metric_filter" "cis_changes_nacl" {
  name           = "CIS-4.11-Changes-NACL"
  pattern        = "{ ($.eventName = CreateNetworkAclEntry) || ($.eventName = DeleteNetworkAcl) || ($.eventName = DeleteNetworkAclEntry) || ($.eventName = ReplaceNetworkAclEntry) || ($.eventName = ReplaceNetworkAclAssociation) }"
  log_group_name = aws_cloudwatch_log_group.CIS_CloudWatch_LogsGroup.name

  metric_transformation {
    name      = "CIS-4.11-Changes-NACL"
    namespace = "CIS_Metric_Alarm_Namespace"
    value     = "1"
  }
}

provider "aws" {
  region = "us-east-2"
}

resource "aws_cloudwatch_log_group" "CIS_CloudWatch_LogsGroup" {
  name = "CIS_CloudWatch_LogsGroup"
}

resource "aws_sns_topic" "cis_alerts_sns_topic" {
  name = "cis-alerts-sns-topic"
}

resource "aws_cloudwatch_metric_alarm" "cis_changes_nacl" {
  alarm_name                = "CIS-4.11-Changes-NACL"
  comparison_operator       = "GreaterThanOrEqualToThreshold"
  evaluation_periods        = "1"
  metric_name               = "OTHER FILTER"
  namespace                 = "CIS_Metric_Alarm_Namespace"
  period                    = "300"
  statistic                 = "Sum"
  threshold                 = "1"
  alarm_actions             = [aws_sns_topic.cis_alerts_sns_topic.arn]
  insufficient_data_actions = []
}

resource "aws_cloudwatch_log_metric_filter" "cis_changes_nacl" {
  name           = "CIS-4.11-Changes-NACL"
  pattern        = "{ ($.eventName = CreateNetworkAcl) || ($.eventName = CreateNetworkAclEntry) || ($.eventName = DeleteNetworkAcl) || ($.eventName = DeleteNetworkAclEntry) || ($.eventName = ReplaceNetworkAclEntry) || ($.eventName = ReplaceNetworkAclAssociation) }"
  log_group_name = aws_cloudwatch_log_group.CIS_CloudWatch_LogsGroup.name

  metric_transformation {
    name      = "CIS-4.11-Changes-NACL"
    namespace = "CIS_Metric_Alarm_Namespace"
    value     = "1"
  }
}