Ensure That the Log Metric Filter and Alerts Exist for Cloud Storage IAM Permission Changes

It is recommended that a metric filter and alarm be established for Cloud Storage Bucket IAM changes. Monitoring changes to cloud storage bucket permissions may reduce the time needed to detect and correct permissions on sensitive cloud storage buckets and objects inside the bucket.

Risk Level: Low
Cloud Entity: GCP AlertPolicy
CloudGuard Rule ID: D9.GCP.LOG.25
Covered by Spectral: No
Category: Management Tools


AlertPolicy where conditions contain [ conditionThreshold.logName] and enabled='true' should have conditions contain [ getResource('LogBasedMetric',conditionThreshold.logName)  getValue('filter') ='resource.type=gcs_bucket AND protoPayload.methodName="storage.setIamPermissions"']


From Portal
Create the prescribed Log Metric:

  1. Go to Logging/Logs-based Metrics by visiting https://console.cloud.google.com/logs/metrics and click "CREATE METRIC".
  2. Select Metric Type as Counter, enter Log metric name and Units to 1.
  3. Clear any text and add:
resource.type=gcs_bucket AND protoPayload.methodName="storage.setIamPermissions"
  1. Click CREATE METRIC. The logs display based on the filter text entered by the user.

Create the prescribed alert policy:

  1. Identify the newly created metric under the section User-defined Metrics at https://console.cloud.google.com/logs/metrics.
  2. Click the 3-dot icon in the rightmost column for the new metric and select 'Create alert from Metric'. A new page appears.
  3. Fill out the alert policy configuration and click Save. Choose the alerting threshold and configuration that makes sense for the user's organization. For example, a threshold of zero(0) for the most recent value will ensure that a notification is triggered for every owner change in the user's project:
  4. Configure the desired notification channels in the section Notifications.
  5. Name the policy and click Save.

From Command Line

  1. Create the prescribed log metric. Reference for command usage: https://cloud.google.com/sdk/gcloud/reference/beta/logging/metrics/create
    use the command:
gcloud beta logging metrics create METRIC_NAME --description="DESCRIPTION" --log-filter="LOG_FILTER"
  1. You can find the notification channel ID using:
gcloud alpha monitoring channels list --filter='displayName="channel_name"' --format='value(name)'
  1. Create the prescribed alert policy.Reference for command usage: https://cloud.google.com/sdk/gcloud/reference/alpha/monitoring/policies/create
  • Create a json file with required properties and values for the policy(try creating a policy from console and then download it's json to have a reference) and use the command:
gcloud alpha monitoring policies create --policy-from-file="policyfile.json"

From TF

  1. Create log based metric with expected filter
  2. Create an alerting policy with type 'metric' based on the previous created log based metric.


See below example;

resource "google_logging_metric" "my_log_metrics" {
	project = "My-project-id"
	name = "my-(custom)/metric"
	filter = resource.type=gcs_bucket AND protoPayload.methodName="storage.setIamPermissions"
	description = "..."
	metric_descriptor {
		metric_kind = "DELTA"
		value_type  = "INT64"


resource "google_monitoring_alert_policy" "alert_policy" {
	project = "My-project-id"
	display_name = "My Alert Policy"
	combiner = "OR"
	conditions {
		display_name = "test condition"
		condition_threshold {
			filter = "metric.type="logging.googleapis.com/user/my-(custom)/metric" AND resource.type="cloud_composer_environment""
			duration   = "0s"
			comparison = "COMPARISON_GT"


  1. https://cloud.google.com/logging/docs/logs-based-metrics/
  2. https://cloud.google.com/monitoring/custom-metrics/
  3. https://cloud.google.com/monitoring/alerts/
  4. https://cloud.google.com/logging/docs/reference/tools/gcloud-logging
  5. https://cloud.google.com/storage/docs/overview
  6. https://cloud.google.com/storage/docs/access-control/iam-roles
  7. https://workbench.cisecurity.org/sections/507170/recommendations/827562

GCP AlertPolicy

Alerting policy describes the circumstances under which you want to be alerted and how you want to be notified. This page provides an overview of alerting policies

Compliance Frameworks

  • CloudGuard GCP All Rules Ruleset
  • GCP CIS Controls V 8
  • GCP CIS Foundations v. 1.0.0
  • GCP CIS Foundations v. 1.1.0
  • GCP CIS Foundations v. 1.2.0
  • GCP CIS Foundations v. 1.3.0
  • GCP CIS Foundations v. 2.0
  • GCP CloudGuard Best Practices
  • GCP MITRE ATT&CK Framework v12.1
  • GCP NIST 800-53 Rev 5