This article contains security recommendations for Blob storage. Implementing these recommendations will help you fulfill your security obligations as described in our shared responsibility model. For more information on what Microsoft does to fulfill service provider responsibilities, read Shared responsibilities for cloud computing.
Some of the recommendations included in this article can be automatically monitored by Azure Security Center. Azure Security Center is the first line of defense in protecting your resources in Azure. For information on Azure Security Center, see the What is Azure Security Center?.
Azure Security Center periodically analyzes the security state of your Azure resources to identify potential security vulnerabilities. It then provides you with recommendations on how to address them. For more information on Azure Security Center recommendations, see Security recommendations in Azure Security Center.
Use the Azure Resource Manager deployment model
Create new storage accounts using the Azure Resource Manager deployment model for important security enhancements, including superior access control (RBAC) and auditing, Resource Manager-based deployment and governance, access to managed identities, access to Azure Key Vault for secrets, and Azure AD-based authentication and authorization for access to Azure Storage data and resources. If possible, migrate existing storage accounts that use the classic deployment model to use Azure Resource Manager. For more information about Azure Resource Manager, see Azure Resource Manager overview.
Enable advanced threat protection for all of your storage accounts
Advanced threat protection for Azure Storage provides an additional layer of security intelligence that detects unusual and potentially harmful attempts to access or exploit storage accounts. Security alerts are triggered in Azure Security Center when anomalies in activity occur and are also sent via email to subscription administrators, with details of suspicious activity and recommendations on how to investigate and remediate threats. For more information, see Advanced threat protection for Azure Storage.
Configure legal holds and time-based retention policies to store blob data in a WORM (Write Once, Read Many) state. Blobs stored immutably can be read, but cannot be modified or deleted for the duration of the retention interval. For more information, see Store business-critical blob data with immutable storage.
Limit shared access signature (SAS) tokens to HTTPS connections only
Keep in mind the principal of least privilege when assigning permissions to an Azure AD security principal via RBAC
When assigning a role to a user, group, or application, grant that security principal only those permissions that are necessary for them to perform their tasks. Limiting access to resources helps prevent both unintentional and malicious misuse of your data.
Use a user delegation SAS to grant limited access to blob data to clients
Secure your account access keys with Azure Key Vault
Microsoft recommends using Azure AD to authorize requests to Azure Storage. However, if you must use Shared Key authorization, then secure your account keys with Azure Key Vault. You can retrieve the keys from the key vault at runtime, instead of saving them with your application. For more information about Azure Key Vault, see Azure Key Vault overview.
Regenerate your account keys periodically
Rotating the account keys periodically reduces the risk of exposing your data to malicious actors.
Keep in mind the principal of least privilege when assigning permissions to a SAS
When creating a SAS, specify only those permissions that are required by the client to perform its function. Limiting access to resources helps prevent both unintentional and malicious misuse of your data.
Have a revocation plan in place for any SAS that you issue to clients
If a SAS is compromised, you will want to revoke that SAS as soon as possible. To revoke a user delegation SAS, revoke the user delegation key to quickly invalidate all signatures associated with that key. To revoke a service SAS that is associated with a stored access policy, you can delete the stored access policy, rename the policy, or change its expiry time to a time that is in the past. For more information, see Grant limited access to Azure Storage resources using shared access signatures (SAS).
If a service SAS is not associated with a stored access policy, then set the expiry time to one hour or less
A service SAS that is not associated with a stored access policy cannot be revoked. For this reason, limiting the expiry time so that the SAS is valid for one hour or less is recommended.
Disable anonymous public read access to containers and blobs
Anonymous public read access to a container and its blobs grants read-only access to those resources to any client. Avoid enabling public read access unless your scenario requires it. To learn how to disable anonymous public access for a storage account, see Configure anonymous public read access for containers and blobs.
Configure the minimum required version of Transport Layer Security (TLS) for a storage account.
Enable the Secure transfer required option on all of your storage accounts
When you enable the Secure transfer required option, all requests made against the storage account must take place over secure connections. Any requests made over HTTP will fail. For more information, see Require secure transfer in Azure Storage.
Configure firewall rules to limit access to your storage account to requests that originate from specified IP addresses or ranges, or from a list of subnets in an Azure Virtual Network (VNet). For more information about configuring firewall rules, see Configure Azure Storage firewalls and virtual networks.
Allow trusted Microsoft services to access the storage account
Turning on firewall rules for your storage account blocks incoming requests for data by default, unless the requests originate from a service operating within an Azure Virtual Network (VNet) or from allowed public IP addresses. Requests that are blocked include those from other Azure services, from the Azure portal, from logging and metrics services, and so on. You can permit requests from other Azure services by adding an exception to allow trusted Microsoft services to access the storage account. For more information about adding an exception for trusted Microsoft services, see Configure Azure Storage firewalls and virtual networks.
A service tag represents a group of IP address prefixes from a given Azure service. Microsoft manages the address prefixes encompassed by the service tag and automatically updates the service tag as addresses change. For more information about service tags supported by Azure Storage, see Azure service tags overview. For a tutorial that shows how to use service tags to create outbound network rules, see Restrict access to PaaS resources.
Limit network access to specific networks
Limiting network access to networks hosting clients requiring access reduces the exposure of your resources to network attacks.
Enable Azure Storage logging to track how each request made against Azure Storage was authorized. The logs indicate whether a request was made anonymously, by using an OAuth 2.0 token, by using Shared Key, or by using a shared access signature (SAS). For more information, see Azure Storage analytics logging.