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Azure security baseline for Functions

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This security baseline applies guidance from the Microsoft cloud security benchmark version 1.0 to Functions. The Microsoft cloud security benchmark provides recommendations on how you can secure your cloud solutions on Azure. The content is grouped by the security controls defined by the Microsoft cloud security benchmark and the related guidance applicable to Functions.

You can monitor this security baseline and its recommendations using Microsoft Defender for Cloud. Azure Policy definitions will be listed in the Regulatory Compliance section of the Microsoft Defender for Cloud portal page.

When a feature has relevant Azure Policy Definitions, they are listed in this baseline to help you measure compliance with the Microsoft cloud security benchmark controls and recommendations. Some recommendations may require a paid Microsoft Defender plan to enable certain security scenarios.

Note

Features not applicable to Functions have been excluded. To see how Functions completely maps to the Microsoft cloud security benchmark, see the full Functions security baseline mapping file.

Security profile

The security profile summarizes high-impact behaviors of Functions, which may result in increased security considerations.

Service Behavior Attribute Value
Product Category Compute, Web
Customer can access HOST / OS No Access
Service can be deployed into customer's virtual network True
Stores customer content at rest True

Network security

For more information, see the Microsoft cloud security benchmark: Network security.

NS-1: Establish network segmentation boundaries

Features

Virtual Network Integration

Description: Service supports deployment into customer's private Virtual Network (VNet). Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Configuration Guidance: Deploy the service into a virtual network. Assign private IPs to the resource (where applicable) unless there is a strong reason to assign public IPs directly to the resource.

Note: Networking features are exposed by the service but need to be configured for the application. By default, public network access is allowed.

Reference: Azure Functions networking options

Network Security Group Support

Description: Service network traffic respects Network Security Groups rule assignment on its subnets. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Configuration Guidance: Use network security groups (NSG) to restrict or monitor traffic by port, protocol, source IP address, or destination IP address. Create NSG rules to restrict your service's open ports (such as preventing management ports from being accessed from untrusted networks). Be aware that by default, NSGs deny all inbound traffic but allow traffic from virtual network and Azure Load Balancers.

Reference: Azure Functions networking options

NS-2: Secure cloud services with network controls

Features

Description: Service native IP filtering capability for filtering network traffic (not to be confused with NSG or Azure Firewall). Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Configuration Guidance: Deploy private endpoints for all Azure resources that support the Private Link feature, to establish a private access point for the resources.

Reference: Azure Functions networking options

Disable Public Network Access

Description: Service supports disabling public network access either through using service-level IP ACL filtering rule (not NSG or Azure Firewall) or using a 'Disable Public Network Access' toggle switch. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Feature notes: Azure Functions can be configured with private endpoints, but there is not presently a single toggle for disabling public network access absent configuring private endpoints.

Configuration Guidance: Disable public network access either using the service-level IP ACL filtering rule or a toggling switch for public network access.

Identity management

For more information, see the Microsoft cloud security benchmark: Identity management.

IM-1: Use centralized identity and authentication system

Features

Azure AD Authentication Required for Data Plane Access

Description: Service supports using Azure AD authentication for data plane access. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Feature notes: Customer-owned endpoints may be configured to require Azure AD authentication requirements. System-provided endpoints for deployment operations and advanced developer tools support Azure AD but by default have the ability to alternatively use publishing credentials. These publishing credentials can be disabled. Some data plane endpoints on the app may be accessed by administrative keys configured in the Functions host, and these are not configurable with Azure AD requirements at this time.

Configuration Guidance: Use Azure Active Directory (Azure AD) as the default authentication method to control your data plane access.

Reference: Configure deployment credentials - disable basic authentication

Local Authentication Methods for Data Plane Access

Description: Local authentications methods supported for data plane access, such as a local username and password. Learn more.

Supported Enabled By Default Configuration Responsibility
True True Microsoft

Feature notes: Deployment credentials are created by default, but they can be disabled. Some operations exposed by the application runtime may be performed using an administrative key, which cannot presently be disabled. This key can be stored in Azure Key Vault, and it can be regenerated at any time. Avoid the usage of local authentication methods or accounts, these should be disabled wherever possible. Instead use Azure AD to authenticate where possible.

Configuration Guidance: No additional configurations are required as this is enabled on a default deployment.

Reference: Disable basic authentication

IM-3: Manage application identities securely and automatically

Features

Managed Identities

Description: Data plane actions support authentication using managed identities. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Configuration Guidance: Use Azure managed identities instead of service principals when possible, which can authenticate to Azure services and resources that support Azure Active Directory (Azure AD) authentication. Managed identity credentials are fully managed, rotated, and protected by the platform, avoiding hard-coded credentials in source code or configuration files.

Reference: How to use managed identities for App Service and Azure Functions

Service Principals

Description: Data plane supports authentication using service principals. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Configuration Guidance: There is no current Microsoft guidance for this feature configuration. Please review and determine if your organization wants to configure this security feature.

Microsoft Defender for Cloud monitoring

Azure Policy built-in definitions - Microsoft.Web:

Name
(Azure portal)		 Description Effect(s) Version
(GitHub)
App Service apps should use managed identity Use a managed identity for enhanced authentication security AuditIfNotExists, Disabled 3.0.0

IM-7: Restrict resource access based on conditions

Features

Conditional Access for Data Plane

Description: Data plane access can be controlled using Azure AD Conditional Access Policies. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Feature notes: For data plane endpoints which are not defined by the application, conditional access would need to be configured against Azure Service Management.

Configuration Guidance: Define the applicable conditions and criteria for Azure Active Directory (Azure AD) conditional access in the workload. Consider common use cases such as blocking or granting access from specific locations, blocking risky sign-in behavior, or requiring organization-managed devices for specific applications.

IM-8: Restrict the exposure of credential and secrets

Features

Service Credential and Secrets Support Integration and Storage in Azure Key Vault

Description: Data plane supports native use of Azure Key Vault for credential and secrets store. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Configuration Guidance: Ensure that secrets and credentials are stored in secure locations such as Azure Key Vault, instead of embedding them into code or configuration files.

Reference: Use Key Vault references for App Service and Azure Functions

Privileged access

For more information, see the Microsoft cloud security benchmark: Privileged access.

PA-1: Separate and limit highly privileged/administrative users

Features

Local Admin Accounts

Description: Service has the concept of a local administrative account. Learn more.

Supported Enabled By Default Configuration Responsibility
False Not Applicable Not Applicable

Configuration Guidance: This feature is not supported to secure this service.

PA-7: Follow just enough administration (least privilege) principle

Features

Azure RBAC for Data Plane

Description: Azure Role-Based Access Control (Azure RBAC) can be used to managed access to service's data plane actions. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Feature notes: The only data-plane actions which can leverage Azure RBAC are the Kudu/SCM/deployment endpoints. These require permission over the Microsoft.Web/sites/publish/Action operation. Endpoints exposed by the customer application itself are not covered by Azure RBAC.

Configuration Guidance: Use Azure role-based access control (Azure RBAC) to manage Azure resource access through built-in role assignments. Azure RBAC roles can be assigned to users, groups, service principals, and managed identities.

Reference: RBAC permissions required to access Kudu

PA-8: Determine access process for cloud provider support

Features

Customer Lockbox

Description: Customer Lockbox can be used for Microsoft support access. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Configuration Guidance: In support scenarios where Microsoft needs to access your data, use Customer Lockbox to review, then approve or reject each of Microsoft's data access requests.

Data protection

For more information, see the Microsoft cloud security benchmark: Data protection.

DP-2: Monitor anomalies and threats targeting sensitive data

Features

Data Leakage/Loss Prevention

Description: Service supports DLP solution to monitor sensitive data movement (in customer's content). Learn more.

Supported Enabled By Default Configuration Responsibility
False Not Applicable Not Applicable

Configuration Guidance: This feature is not supported to secure this service.

DP-3: Encrypt sensitive data in transit

Features

Data in Transit Encryption

Description: Service supports data in-transit encryption for data plane. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Feature notes: Function apps are created by default to support TLS 1.2 as a minimum version, but an app can be configured with a lower version through a configuration setting. HTTPS is not required of incoming requests by default, but this can also be set via a configuration setting, at which point any HTTP request will be automatically redirected to use HTTPS.

Configuration Guidance: Enable secure transfer in services where there is a native data in transit encryption feature built in. Enforce HTTPS on any web applications and services and ensure TLS v1.2 or later is used. Legacy versions such as SSL 3.0, TLS v1.0 should be disabled. For remote management of Virtual Machines, use SSH (for Linux) or RDP/TLS (for Windows) instead of an unencrypted protocol.

Reference: Add and manage TLS/SSL certificates in Azure App Service

Microsoft Defender for Cloud monitoring

Azure Policy built-in definitions - Microsoft.Web:

Name
(Azure portal)		 Description Effect(s) Version
(GitHub)
App Service apps should only be accessible over HTTPS Use of HTTPS ensures server/service authentication and protects data in transit from network layer eavesdropping attacks. Audit, Disabled, Deny 4.0.0

DP-4: Enable data at rest encryption by default

Features

Data at Rest Encryption Using Platform Keys

Description: Data at-rest encryption using platform keys is supported, any customer content at rest is encrypted with these Microsoft managed keys. Learn more.

Supported Enabled By Default Configuration Responsibility
True True Microsoft

Configuration Guidance: No additional configurations are required as this is enabled on a default deployment.

DP-5: Use customer-managed key option in data at rest encryption when required

Features

Data at Rest Encryption Using CMK

Description: Data at-rest encryption using customer-managed keys is supported for customer content stored by the service. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Feature notes: Azure Functions does not directly support this feature, but an application can be configured to leverage services which do, in place of any possible data storage in Functions. Azure Files may be mounted as the file system, all App Settings, including secrets, may be stored in Azure Key Vault, and deployment options such as run-from-package may pull content from Azure Blob storage.

Configuration Guidance: If required for regulatory compliance, define the use case and service scope where encryption using customer-managed keys are needed. Enable and implement data at rest encryption using customer-managed key for those services.

Reference: Encrypt your application data at rest using customer-managed keys

DP-6: Use a secure key management process

Features

Key Management in Azure Key Vault

Description: The service supports Azure Key Vault integration for any customer keys, secrets, or certificates. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Configuration Guidance: Use Azure Key Vault to create and control the life cycle of your encryption keys, including key generation, distribution, and storage. Rotate and revoke your keys in Azure Key Vault and your service based on a defined schedule or when there is a key retirement or compromise. When there is a need to use customer-managed key (CMK) in the workload, service, or application level, ensure you follow the best practices for key management: Use a key hierarchy to generate a separate data encryption key (DEK) with your key encryption key (KEK) in your key vault. Ensure keys are registered with Azure Key Vault and referenced via key IDs from the service or application. If you need to bring your own key (BYOK) to the service (such as importing HSM-protected keys from your on-premises HSMs into Azure Key Vault), follow recommended guidelines to perform initial key generation and key transfer.

Reference: Use Key Vault references for App Service and Azure Functions

DP-7: Use a secure certificate management process

Features

Certificate Management in Azure Key Vault

Description: The service supports Azure Key Vault integration for any customer certificates. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Configuration Guidance: Use Azure Key Vault to create and control the certificate lifecycle, including creation, importing, rotation, revocation, storage, and purging of the certificate. Ensure the certificate generation follows defined standards without using any insecure properties, such as: insufficient key size, overly long validity period, insecure cryptography. Setup automatic rotation of the certificate in Azure Key Vault and the Azure service (if supported) based on a defined schedule or when there is a certificate expiration. If automatic rotation is not supported in the application, ensure they are still rotated using manual methods in Azure Key Vault and the application.

Reference: Add a TLS/SSL certificate in Azure App Service

Asset management

For more information, see the Microsoft cloud security benchmark: Asset management.

AM-2: Use only approved services

Features

Azure Policy Support

Description: Service configurations can be monitored and enforced via Azure Policy. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Configuration Guidance: Use Microsoft Defender for Cloud to configure Azure Policy to audit and enforce configurations of your Azure resources. Use Azure Monitor to create alerts when there is a configuration deviation detected on the resources. Use Azure Policy [deny] and [deploy if not exists] effects to enforce secure configuration across Azure resources.

Logging and threat detection

For more information, see the Microsoft cloud security benchmark: Logging and threat detection.

LT-1: Enable threat detection capabilities

Features

Microsoft Defender for Service / Product Offering

Description: Service has an offering-specific Microsoft Defender solution to monitor and alert on security issues. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Feature notes: Defender for App Service includes Azure Functions. If this solution is enabled, function apps under the enablement scope will be included.

Configuration Guidance: Use Azure Active Directory (Azure AD) as the default authentication method to control your management plane access. When you get an alert from Microsoft Defender for Key Vault, investigate and respond to the alert.

Reference: Defender for App Service

LT-4: Enable logging for security investigation

Features

Azure Resource Logs

Description: Service produces resource logs that can provide enhanced service-specific metrics and logging. The customer can configure these resource logs and send them to their own data sink like a storage account or log analytics workspace. Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Configuration Guidance: Enable resource logs for the service. For example, Key Vault supports additional resource logs for actions that get a secret from a key vault or and Azure SQL has resource logs that track requests to a database. The content of resource logs varies by the Azure service and resource type.

Reference: Monitoring Azure Functions with Azure Monitor Logs

Backup and recovery

For more information, see the Microsoft cloud security benchmark: Backup and recovery.

BR-1: Ensure regular automated backups

Features

Azure Backup

Description: The service can be backed up by the Azure Backup service. Learn more.

Supported Enabled By Default Configuration Responsibility
False Not Applicable Not Applicable

Feature notes: A feature for backing up an application is available if hosted on a Standard, Premium, or Isolated App Service plan. This feature does not leverage Azure Backup and does not include event sources or externally linked storage. See /azure/app-service/manage-backup for more details.

Configuration Guidance: This feature is not supported to secure this service.

Service Native Backup Capability

Description: Service supports its own native backup capability (if not using Azure Backup). Learn more.

Supported Enabled By Default Configuration Responsibility
True False Customer

Feature notes: A backup feature is available to apps running on Standard, Premium, and Isolated App Service plans. This does not include backing up event sources or externally provided storage.

Configuration Guidance: There is no current Microsoft guidance for this feature configuration. Please review and determine if your organization wants to configure this security feature.

Reference: Back up and restore your app in Azure App Service

Next steps