Cis GCP Foundations 2.10

2.10 Ensure That the Log Metric Filter and Alerts Exist for Cloud Storage IAM Permission Changes (Automated)

Profile Applicability

• Level 2

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 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 at 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

Remediation

From Google Cloud Console

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. Click the down arrow symbol on the Filter Bar at the rightmost corner and select Convert to Advanced Filter.
3. Clear any text and add:

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

4. Click Submit Filter. Display logs appear based on the filter text entered by the user.
5. In the Metric Editor menu on right, fill out the name field. Set Units to 1 (default) and Type to Counter. This ensures that the log metric counts the number of log entries matching the user's advanced logs query.
6. Click Create Metric.

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 project:

Set `Aggregator` to `Count`

Set `Configuration`:
- Condition: above
- Threshold: 0
- For: most recent value

4. Configure the desired notifications channels in the section Notifications.
5. Name the policy and click Save.

From Google Cloud CLI

Create the prescribed Log Metric:

• Use the command: gcloud beta logging metrics create

Create the prescribed alert policy:

• Use the command: gcloud alpha monitoring policies create

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

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