Information
Database Server should accept connections only from trusted Network(s)/IP(s) and restrict access from public IP addresses.
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.
Solution
From Google Cloud Console
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Go to the Cloud SQL Instances page in the Google Cloud Console by visiting https://console.cloud.google.com/sql/instances .
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Click the instance name to open its Instance details page.
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Under the Configuration section click Edit configurations
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Under Configuration options expand the Connectivity section.
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Click the delete icon for the authorized network 0.0.0.0/0
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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 .
Impact:
The Cloud SQL database instance would not be available to public IP addresses.