Information
Database Server should accept connections only from trusted Network(s)/IP(s) and restrict access from public IP addresses.
Rationale:
To minimize attack surface on a Database server instance, only trusted/known and required IP(s) should be white-listed to connect to it.
An authorized network should not have IPs/networks configured to 0.0.0.0/0 which will allow access to the instance from anywhere in the world. Note that authorized networks apply only to instances with public IPs.
Impact:
The Cloud SQL database instance would not be available to public IP addresses.
Solution
From Google Cloud Console
Go to the Cloud SQL Instances page in the Google Cloud Console by visiting https://console.cloud.google.com/sql/instances.
Click the instance name to open its Instance details page.
Under the Configuration section click Edit configurations
Under Configuration options expand the Connectivity section.
Click the delete icon for the authorized network 0.0.0.0/0.
Click Save to update the instance.
From Google Cloud CLI
Update the authorized network list by dropping off any addresses.
gcloud sql instances patch <INSTANCE_NAME> --authorized-networks=IP_ADDR1,IP_ADDR2...
Prevention:
To prevent new SQL instances from being configured to accept incoming connections from any IP addresses, set up a Restrict Authorized Networks on Cloud SQL instances Organization Policy at: https://console.cloud.google.com/iam-admin/orgpolicies/sql-restrictAuthorizedNetworks.
Default Value:
By default, authorized networks are not configured. Remote connection to Cloud SQL database instance is not possible unless authorized networks are configured.