# Ensure a log metric filter and alarm exist for changes to network gateways - Source: https://support.icompaas.com/support/solutions/articles/a_1793292193807843-ensure-a-log-metric-filter-and-alarm-exist-for-changes-to-network-gateways - Section: [Solutions](https://support.icompaas.com/support/solutions) › [AWS_Checks_v5.39.1](https://support.icompaas.com/support/solutions/c_1793285913477877) › [AWS Checks](https://support.icompaas.com/support/solutions/folders/f_1793287194371224) - Last updated: 2026-10-29 - Publisher: iCompaas, Inc. (https://www.icompaas.com) **Description** Ensure that AWS CloudTrail events are sent to Amazon CloudWatch Logs and that the trail's log group has a metric filter with an associated CloudWatch alarm for changes to network gateways. It covers the creation and deletion of customer gateways and the creation, deletion, attachment and detachment of internet gateways. The alarm notifies responders whenever a matching event is recorded. **Rationale** Network gateways are required to send and receive traffic to and from destinations outside a VPC. Without monitoring, an unauthorized or accidental gateway change can expose private networks to the Internet, allow data to leave the VPC without inspection, or break connectivity, and go unnoticed. An alarm on these events lets the security team review every gateway change quickly. Gateway changes should also be limited to authorized administrators and require change approval. **Impact** - Provides near real-time alerts when customer gateways or internet gateways are created, deleted, attached or detached - No effect on running workloads; the filter and alarm only read CloudTrail events - Adds a small cost for the CloudWatch alarm, and for CloudWatch Logs ingestion if CloudTrail was not already sending events to CloudWatch Logs **Default Value** No metric filters or CloudWatch alarms exist by default. A CloudTrail trail does not send events to CloudWatch Logs unless this is configured on the trail. **Pre-Requisites** - IAM permissions: cloudtrail:DescribeTrails, cloudtrail:UpdateTrail, logs:DescribeMetricFilters, logs:PutMetricFilter, cloudwatch:DescribeAlarmsForMetric, cloudwatch:PutMetricAlarm, plus logs:DeleteMetricFilter and cloudwatch:DeleteAlarms for the backout plan - A CloudTrail trail, preferably multi-region, that sends its events to a CloudWatch Logs log group - An Amazon SNS topic with confirmed subscribers (for example, the security team's email address) to receive the alarm notifications **Remediation** **Test Plan** **Console:** 1. Sign in to the AWS Management Console at [https://console.aws.amazon.com](https://console.aws.amazon.com/). 2. Open the AWS CloudTrail console and select **Trails**. 3. Open each trail and, in the **CloudWatch Logs** section, note the log group the trail sends events to. 4. Open the Amazon CloudWatch console in the region of that log group, choose **Log groups** and select the log group. 5. Open the **Metric filters** tab and check for a filter whose pattern includes all of these events: CreateCustomerGateway, DeleteCustomerGateway, AttachInternetGateway, CreateInternetGateway, DeleteInternetGateway and DetachInternetGateway. 6. Note the metric name of that filter, then choose **Alarms**, **All alarms** and check that an alarm exists for that metric. 7. If no trail's log group has such a metric filter with an alarm, follow the implementation steps. **CLI:** List the trails and the CloudWatch Logs log group each one sends events to: aws cloudtrail describe-trails --region --query "trailList\[\].\[Name,HomeRegion,IsMultiRegionTrail,CloudWatchLogsLogGroupArn\]" --output table List the metric filters of the log group (the name after log-group: in the ARN), in the region of the log group: aws logs describe-metric-filters --region --log-group-name --query "metricFilters\[\].\[filterName,filterPattern,metricTransformations\[0\].metricName,metricTransformations\[0\].metricNamespace\]" --output table List the alarms on the metric of the matching filter: aws cloudwatch describe-alarms-for-metric --region --metric-name --namespace --query "MetricAlarms\[\].\[AlarmName,StateValue,ActionsEnabled\]" --output table The account fails if no trail sends events to a log group, if no metric filter on a trail's log group has a pattern that includes every event listed above, or if no alarm exists for the metric of that filter. **Implementation Steps** **Console:** 1. Sign in to the AWS Management Console at [https://console.aws.amazon.com](https://console.aws.amazon.com/). 2. If no trail sends events to CloudWatch Logs, open the AWS CloudTrail console, open a multi-region trail, choose **Edit** in the **CloudWatch Logs** section, enable it, select or create a log group and an IAM role, and save the changes. 3. Open the Amazon CloudWatch console in the region of the trail's log group, choose **Log groups** and select the log group. 4. Open the **Metric filters** tab and choose **Create metric filter**. 5. In **Filter pattern**, enter { ($.eventName = CreateCustomerGateway) || ($.eventName = DeleteCustomerGateway) || ($.eventName = AttachInternetGateway) || ($.eventName = CreateInternetGateway) || ($.eventName = DeleteInternetGateway) || ($.eventName = DetachInternetGateway) } and choose **Next**. 6. Enter the metric details and choose **Next**: - **Filter name**: network\_gw\_changes - **Metric namespace**: CISBenchmark - **Metric name**: network\_gw\_changes\_metric - **Metric value**: 1 7. Choose **Create metric filter**. 8. On the **Metric filters** tab, select the new filter and choose **Create alarm**. 9. Set the metric and conditions, then choose **Next**: - **Statistic**: **Sum** - **Period**: **5 minutes** - **Threshold type**: **Static**, **Greater/Equal**, 1 10. Under **Notification**, select the SNS topic that alerts the security team and choose **Next**. 11. Enter the alarm name network\_gw\_changes\_alarm, choose **Next**, then **Create alarm**. **Backout Plan** 1. Sign in to the AWS Management Console at [https://console.aws.amazon.com](https://console.aws.amazon.com/). 2. Open the Amazon CloudWatch console, choose **Alarms**, **All alarms**, select the network\_gw\_changes\_alarm alarm and delete it. 3. Choose **Log groups**, select the trail's log group, open the **Metric filters** tab, select the network\_gw\_changes filter and delete it. **CLI:** aws cloudwatch delete-alarms --region --alarm-names network\_gw\_changes\_alarm aws logs delete-metric-filter --region --log-group-name --filter-name network\_gw\_changes Note: removing the metric filter and alarm stops alerts for changes to network gateways, so these events can again go unnoticed. **Reference** - [https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.html](https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudwatch-alarms-for-cloudtrail.html) - [https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/Alarm-On-Logs.html](https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/Alarm-On-Logs.html) - [https://docs.aws.amazon.com/cli/latest/reference/logs/describe-metric-filters.html](https://docs.aws.amazon.com/cli/latest/reference/logs/describe-metric-filters.html) ## Related compliance guidance - [SOC 2 compliance: a practical implementation guide for cloud-native SaaS teams](https://support.icompaas.com/compliance/soc-2-trust-services-criteria): Configuration checks like this one are the technical half of a SOC 2 / ISO 27001 programme — the guide shows where they fit, what else an auditor expects, and how to evidence them. - [ISO/IEC 27001:2022 compliance: a practical implementation guide](https://support.icompaas.com/compliance/iso-27001-2022): ISO 27001 Annex A.8 (technological controls) is where cloud hardening evidence lands; the guide shows how to run the ISMS around it.