Description:

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


Rationale:

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.


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 dded in Firewall Policy.


Audit:

From Azure Portal

1. Go to SQL servers

2. For each SQL server

3. Click on Networking

4. Ensure that Allow Azure services and resources to access this server is Unchecked

5. Ensure that no firewall rule exists with

• Start IP of 0.0.0.0

• or other combinations which allows access to wider public IP ranges


From Azure CLI

List all SQL servers

az sql server list

For each SQL server run the following command

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

Ensure the output does not contain any firewall allow rules with a source of 0.0.0.0, or

any rules named AllowAllWindowsAzureIps


From PowerShell

Get the list of all SQL Servers

Get-AzSqlServer

For each Server

Get-AzSqlServerFirewallRule -ResourceGroupName <resource group name> - ServerName <server name>

Ensure that StartIpAddress is not set to 0.0.0.0, /0 or other combinations which allows access to wider public IP ranges including Windows Azure IP ranges. Also ensure that FirewallRuleName doesn't contain AllowAllWindowsAzureIps which is the rule created when the Allow Azure services and resources to access this server setting is enabled for that SQL Server.


Remediation:

From Azure Portal

1. Go to SQL servers

2. For each SQL server

3. Click on Networking

4. Uncheck the checkbox for Allow Azure services and resources to access this server

5. Set firewall rules to limit access to only authorized connections


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.

References:

  1. https://docs.microsoft.com/en-us/sql/database-engine/configurewindows/configure-a-windows-firewall-for-database engine-access?view=sqlserver-2017
  2. https://docs.microsoft.com/en-us/powershell/module/azurerm.sql/getazurermsqlserverfirewallrule?view=azurermps-5.2.0
  3. https://docs.microsoft.com/en-us/powershell/module/azurerm.sql/removeazurermsqlserverfirewallrule?view=azurermps5.2.0
  4. https://docs.microsoft.com/en-us/azure/sql-database/sql-database-firewallconfigure