Ensure no SQL Databases allow ingress 0.0.0.0/0 (ANY IP)

Description:

Ensure that no SQL Databases allow ingress from 0.0.0.0/0 (ANY IP).

Rationale:

SQL Server includes a firewall to block access to unauthorized connections. More granular IP addresses can be defined by referencing the range of addresses available from specific datacenters.

By default, for a SQL server, a Firewall exists with StartIp of 0.0.0.0 and EndIP of 0.0.0.0 allowing access to all the Azure services.

Additionally, a custom rule can be set up with StartIp of 0.0.0.0 and EndIP of 255.255.255.255 allowing access from ANY IP over the Internet.

In order to reduce the potential attack surface for a SQL server, firewall rules should be defined with more granular IP addresses by referencing the range of addresses available from specific datacenters.

Impact: Disabling 'Allow Azure services and resources to access this server' will break all connections to SQL server and Hosted Databases unless custom IP specific rules are not added in Firewall Policy.

From Azure Console

1. Go to 'SQL servers'
2. For each SQL server
3. Click on 'Firewall and virtual networks'
4. Set 'Allow Azure services and resources to access this server' to 'No'
5. Set firewall rules to limit access to only authorized connections

Using Azure PowerShell

Disable Default Firewall Rule 'Allow access to Azure services' :

Remove-AzureRmSqlServerFirewallRule -FirewallRuleName "AllowAllWindowsAzureIps" -ResourceGroupName -ServerName

Remove custom Firewall rule:
Remove-AzureRmSqlServerFirewallRule -FirewallRuleName "" -ResourceGroupName -ServerName

Set the appropriate firewall rules:

Set-AzureRmSqlServerFirewallRule -ResourceGroupName -ServerName -FirewallRuleName "" -StartIpAddress "<IP Address other than 0.0.0.0>" -EndIpAddress "<IP Address other than 0.0.0.0 or 255.255.255.255>"
.