Set up Azure App Service access restrictions

By setting up access restrictions, you can define a priority-ordered allow/deny list that controls network access to your app. The list can include IP addresses or Azure Virtual Network subnets. When there are one or more entries, an implicit deny all exists at the end of the list.

The access restriction capability works with all Azure App Service-hosted workloads. The workloads can include web apps, API apps, Linux apps, Linux container apps, and Functions.

When a request is made to your app, the FROM address is evaluated against the rules in your access restriction list. If the FROM address is in a subnet that's configured with service endpoints to Microsoft.Web, the source subnet is compared against the virtual network rules in your access restriction list. If the address isn't allowed access based on the rules in the list, the service replies with an HTTP 403 status code.

The access restriction capability is implemented in the App Service front-end roles, which are upstream of the worker hosts where your code runs. Therefore, access restrictions are effectively network access-control lists (ACLs).

The ability to restrict access to your web app from an Azure virtual network is enabled by service endpoints. With service endpoints, you can restrict access to a multi-tenant service from selected subnets. It doesn't work to restrict traffic to apps that are hosted in an App Service Environment. If you're in an App Service Environment, you can control access to your app by applying IP address rules.

Note

The service endpoints must be enabled both on the networking side and for the Azure service that they're being enabled with. For a list of Azure services that support service endpoints, see Virtual Network service endpoints.

Diagram of the flow of access restrictions.

Manage access restriction rules in the portal

To add an access restriction rule to your app, do the following:

  1. Sign in to the Azure portal.

  2. On the left pane, select Networking.

  3. On the Networking pane, under Access Restrictions, select Configure Access Restrictions.

    Screenshot of the App Service networking options pane in the Azure portal.

  4. On the Access Restrictions page, review the list of access restriction rules that are defined for your app.

    Screenshot of the Access Restrictions page in the Azure portal, showing the list of access restriction rules defined for the selected app.

    The list displays all the current restrictions that are applied to the app. If you have a virtual network restriction on your app, the table shows whether the service endpoints are enabled for Microsoft.Web. If no restrictions are defined on your app, the app is accessible from anywhere.

Add an access restriction rule

To add an access restriction rule to your app, on the Access Restrictions pane, select Add rule. After you add a rule, it becomes effective immediately.

Rules are enforced in priority order, starting from the lowest number in the Priority column. An implicit deny all is in effect after you add even a single rule.

On the Add Access Restriction pane, when you create a rule, do the following:

  1. Under Action, select either Allow or Deny.

    Screenshot of the 'Add Access Restriction' pane.

  2. Optionally, enter a name and description of the rule.

  3. In the Priority box, enter a priority value.

  4. In the Type drop-down list, select the type of rule.

The different types of rules are described in the following sections.

Note

  • There is a limit of 512 access restriction rules. If you require more than 512 access restriction rules, we suggest that you consider installing a standalone security product, such as Azure Front Door, Azure App Gateway, or an alternative WAF.

Set an IP address-based rule

Follow the procedure as outlined in the preceding section, but with the following addition:

  • For step 4, in the Type drop-down list, select IPv4 or IPv6.

Specify the IP Address Block in Classless Inter-Domain Routing (CIDR) notation for both the IPv4 and IPv6 addresses. To specify an address, you can use something like 1.2.3.4/32, where the first four octets represent your IP address and /32 is the mask. The IPv4 CIDR notation for all addresses is 0.0.0.0/0. To learn more about CIDR notation, see Classless Inter-Domain Routing.

Set a service endpoint-based rule

  • For step 4, in the Type drop-down list, select Virtual Network.

    Screenshot of the 'Add Restriction' pane with the Virtual Network type selected.

Specify the Subscription, Virtual Network, and Subnet drop-down lists, matching what you want to restrict access to.

By using service endpoints, you can restrict access to selected Azure virtual network subnets. If service endpoints aren't already enabled with Microsoft.Web for the subnet that you selected, they'll be automatically enabled unless you select the Ignore missing Microsoft.Web service endpoints check box. The scenario where you might want to enable service endpoints on the app but not the subnet depends mainly on whether you have the permissions to enable them on the subnet.

If you need someone else to enable service endpoints on the subnet, select the Ignore missing Microsoft.Web service endpoints check box. Your app will be configured for service endpoints in anticipation of having them enabled later on the subnet.

You can't use service endpoints to restrict access to apps that run in an App Service Environment. When your app is in an App Service Environment, you can control access to it by applying IP access rules.

With service endpoints, you can configure your app with application gateways or other web application firewall (WAF) devices. You can also configure multi-tier applications with secure back ends. For more information, see Networking features and App Service and Application Gateway integration with service endpoints.

Note

  • Service endpoints aren't currently supported for web apps that use IP-based TLS/SSL bindings with a virtual IP (VIP).

Set a service tag-based rule

  • For step 4, in the Type drop-down list, select Service Tag.

    Screenshot of the 'Add Restriction' pane with the Service Tag type selected.

Each service tag represents a list of IP ranges from Azure services. A list of these services and links to the specific ranges can be found in the service tag documentation.

All available service tags are supported in access restriction rules. For simplicity, only a list of the most common tags are available through the Azure portal. Use Azure Resource Manager templates or scripting to configure more advanced rules like regional scoped rules. These are the tags available through Azure portal:

  • ActionGroup
  • ApplicationInsightsAvailability
  • AzureCloud
  • AzureCognitiveSearch
  • AzureEventGrid
  • AzureFrontDoor.Backend
  • AzureMachineLearning
  • AzureTrafficManager
  • LogicApps

Edit a rule

  1. To begin editing an existing access restriction rule, on the Access Restrictions page, select the rule you want to edit.

  2. On the Edit Access Restriction pane, make your changes, and then select Update rule. Edits are effective immediately, including changes in priority ordering.

    Screenshot of the 'Edit Access Restriction' pane in the Azure portal, showing the fields for an existing access restriction rule.

    Note

    When you edit a rule, you can't switch between rule types.

Delete a rule

To delete a rule, on the Access Restrictions page, select the ellipsis (...) next to the rule you want to delete, and then select Remove.

Screenshot of the 'Access Restrictions' page, showing the 'Remove' ellipsis next to the access restriction rule to be deleted.

Access restriction advanced scenarios

The following sections describe some advanced scenarios using access restrictions.

Filter by http header

As part of any rule, you can add additional http header filters. The following http header names are supported:

  • X-Forwarded-For
  • X-Forwarded-Host
  • X-Azure-FDID
  • X-FD-HealthProbe

For each header name, you can add up to eight values separated by comma. The http header filters are evaluated after the rule itself and both conditions must be true for the rule to apply.

Multi-source rules

Multi-source rules allow you to combine up to eight IP ranges or eight Service Tags in a single rule. You might use this if you have more than 512 IP ranges or you want to create logical rules where multiple IP ranges are combined with a single http header filter.

Multi-source rules are defined the same way you define single-source rules, but with each range separated with comma.

PowerShell example:

Add-AzWebAppAccessRestrictionRule -ResourceGroupName "ResourceGroup" -WebAppName "AppName" `
  -Name "Multi-source rule" -IpAddress "192.168.1.0/24,192.168.10.0/24,192.168.100.0/24" `
  -Priority 100 -Action Allow

Block a single IP address

When you add your first access restriction rule, the service adds an explicit Deny all rule with a priority of 2147483647. In practice, the explicit Deny all rule is the final rule to be executed, and it blocks access to any IP address that's not explicitly allowed by an Allow rule.

For a scenario where you want to explicitly block a single IP address or a block of IP addresses, but allow access to everything else, add an explicit Allow All rule.

Screenshot of the 'Access Restrictions' page in the Azure portal, showing a single blocked IP address.

Restrict access to an SCM site

In addition to being able to control access to your app, you can restrict access to the SCM site that's used by your app. The SCM site is both the web deploy endpoint and the Kudu console. You can assign access restrictions to the SCM site from the app separately or use the same set of restrictions for both the app and the SCM site. When you select the Same restrictions as <app name> check box, everything is blanked out. If you clear the check box, your SCM site settings are reapplied.

Screenshot of the 'Access Restrictions' page in the Azure portal, showing that no access restrictions are set for the SCM site or the app.

Restrict access to a specific Azure Front Door instance

Traffic from Azure Front Door to your application originates from a well known set of IP ranges defined in the AzureFrontDoor.Backend service tag. Using a service tag restriction rule, you can restrict traffic to only originate from Azure Front Door. To ensure traffic only originates from your specific instance, you will need to further filter the incoming requests based on the unique http header that Azure Front Door sends.

Screenshot of the 'Access Restrictions' page in the Azure portal, showing how to add Azure Front Door restriction.

PowerShell example:

$afd = Get-AzFrontDoor -Name "MyFrontDoorInstanceName"
Add-AzWebAppAccessRestrictionRule -ResourceGroupName "ResourceGroup" -WebAppName "AppName" `
  -Name "Front Door example rule" -Priority 100 -Action Allow -ServiceTag AzureFrontDoor.Backend `
  -HttpHeader @{'x-azure-fdid' = $afd.FrontDoorId}

Manage access restriction rules programmatically

You can add access restrictions programmatically by doing either of the following:

  • Use the Azure CLI. For example:

    az webapp config access-restriction add --resource-group ResourceGroup --name AppName \
      --rule-name 'IP example rule' --action Allow --ip-address 122.133.144.0/24 --priority 100
    

    Note

    Working with service tags, http headers or multi-source rules in Azure CLI requires at least version 2.23.0. You can verify the version of the installed module with: az version

  • Use Azure PowerShell. For example:

    Add-AzWebAppAccessRestrictionRule -ResourceGroupName "ResourceGroup" -WebAppName "AppName"
        -Name "Ip example rule" -Priority 100 -Action Allow -IpAddress 122.133.144.0/24
    

    Note

    Working with service tags, http headers or multi-source rules in Azure PowerShell requires at least version 5.7.0. You can verify the version of the installed module with: Get-InstalledModule -Name Az

You can also set values manually by doing either of the following:

  • Use an Azure REST API PUT operation on the app configuration in Azure Resource Manager. The location for this information in Azure Resource Manager is:

    management.azure.com/subscriptions/subscription ID/resourceGroups/resource groups/providers/Microsoft.Web/sites/web app name/config/web?api-version=2020-06-01

  • Use a Resource Manager template. As an example, you can use resources.azure.com and edit the ipSecurityRestrictions block to add the required JSON.

    The JSON syntax for the earlier example is:

    {
      "properties": {
        "ipSecurityRestrictions": [
          {
            "ipAddress": "122.133.144.0/24",
            "action": "Allow",
            "priority": 100,
            "name": "IP example rule"
          }
        ]
      }
    }
    

    The JSON syntax for an advanced example using service tag and http header restriction is:

    {
      "properties": {
        "ipSecurityRestrictions": [
          {
            "ipAddress": "AzureFrontDoor.Backend",
            "tag": "ServiceTag",
            "action": "Allow",
            "priority": 100,
            "name": "Azure Front Door example",
            "headers": {
              "x-azure-fdid": [
                "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
              ]
            }
          }
        ]
      }
    }
    

Set up Azure Functions access restrictions

Access restrictions are also available for function apps with the same functionality as App Service plans. When you enable access restrictions, you also disable the Azure portal code editor for any disallowed IPs.

Next steps

Access restrictions for Azure Functions
Application Gateway integration with service endpoints