Control: 5.1.2 Ensure no Azure SQL Databases allow ingress from 0.0.0.0/0 (ANY IP)

Description

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

Azure 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.

If Allow Azure services and resources to access this server is 'Checked', this will allow resources outside of the subscription/tenant/organization boundary, within any region of Azure, to effectively bypass the defined SQL Server Network ACL on public endpoint. A malicious attacker can successfully launch a SQL server password bruteforce attack by creating a virtual machine in any Azure subscription/region, from outside of the subscription boundary where the SQL Server is residing.

Remediation

From Azure Portal

1. Go to SQL servers.
2. For each SQL server.
3. Under Security, click Networking.
4. Uncheck Allow Azure services and resources to access this server.
5. Set firewall rules to limit access to only authorized connections.
6. Click Save.

From Azure CLI

Disable default firewall rule Allow access to Azure services:

az sql server firewall-rule delete --resource-group <resource group> --server <sql server name> --name "AllowAllWindowsAzureIps"

Remove a custom firewall rule:

az sql server firewall-rule delete --resource-group <resource group> --server <sql server name> --name <firewall rule name>

Create a firewall rule:

az sql server firewall-rule create --resource-group <resource group> --server <sql server name> --name <firewall rule name> --start-ip-address "<IP Address other than 0.0.0.0>" --end-ip-address "<IP Address other than 0.0.0.0 or 255.255.255.255>"

Update a firewall rule:

az sql server firewall-rule update --resource-group <resource group> --server <sql server name> --name <firewall rule name> --start-ip-address "<IP Address other than 0.0.0.0>" --end-ip-address "<IP Address other than 0.0.0.0 or 255.255.255.255>"

From PowerShell

Disable Default Firewall Rule Allow access to Azure services:

Remove-AzSqlServerFirewallRule -FirewallRuleName "AllowAllWindowsAzureIps" -ResourceGroupName <resource group name> -ServerName <server name>

Remove a custom Firewall rule:

Remove-AzSqlServerFirewallRule -FirewallRuleName "<firewall rule name>" -ResourceGroupName <resource group name> -ServerName <server name>

Set the appropriate firewall rules:

Set-AzSqlServerFirewallRule -ResourceGroupName <resource group name> -ServerName <server name> -FirewallRuleName "<firewall rule name>" -StartIpAddress "<IP Address other than 0.0.0.0>" -EndIpAddress "<IP Address other than 0.0.0.0 or 255.255.255.255>"

Default Value

By default, Allow access to Azure Services is set to NO.