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Description

It is recommended that a metric filter and alarm be established for Cloud Storage Bucket IAM changes.

Rationale​

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.

Impact​

Enabling of logging may result in your project being charged for the additional logs usage. These charges could be significant depending on the size of the organization.

Audit​

From Google Cloud Console​

Ensure the prescribed log metric is present:

  1. For each project that contains cloud storage buckets, go to Logging/Logs-based Metrics by visiting https://console.cloud.google.com/logs/metrics.

  2. In the User-defined Metrics section, ensure at least one metric <Log_Metric_Name> is present with the filter text:

         resource.type="gcs_bucket" 
         AND protoPayload.methodName="storage.setIamPermissions"

    Ensure that the prescribed alerting policy is present:

  3. Go to Alerting by visiting https://console.cloud.google.com/monitoring/alerting.

  4. Under the Policies section, ensure that at least one alert policy exists for the log metric above. Clicking on the policy should show that it is configured with a condition. For example, Violates when: Any logging.googleapis.com/user/<Log Metric Name> stream is above a threshold of 0 for greater than 0 seconds means that the alert will trigger for any new owner change. Verify that the chosen alerting thresholds make sense for the user's organization.

  5. Ensure that the appropriate notifications channels have been set up.

From Google Cloud CLI​

Ensure that the prescribed log metric is present:

  1. List the log metrics:

         gcloud logging metrics list --format json

  2. Ensure that the output contains at least one metric with the filter set to:

         resource.type=gcs_bucket 
         AND protoPayload.methodName="storage.setIamPermissions"

  3. Note the value of the property metricDescriptor.type for the identified metric, in the format logging.googleapis.com/user/<Log Metric Name>.

    Ensure the prescribed alerting policy is present:

  4. List the alerting policies:

         gcloud alpha monitoring policies list --format json

  5. Ensure that the output contains an least one alert policy where:

    • conditions.conditionThreshold.filter is set to metric.type=\"logging.googleapis.com/user/<Log Metric Name>\"

    • AND enabled is set to true

References​

  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