A company stores sensitive files in Azure Files shares. They require that data is encrypted at rest using a customer-managed key (CMK) stored in Azure Key Vault, and that all client connections use SMB 3.0 encryption for end-to-end encryption in transit. They create a premium Azure Files share in a storage account and configure encryption at rest with a CMK. However, clients are unable to connect without SMB encryption. What additional configuration is necessary to enforce SMB encryption for all connections?
Trap 1: No additional configuration is needed; Azure Files uses SMB…
Azure Files does support SMB 3.0 encryption, but the protocol version and encryption are not mandatory by default; the storage account will accept unencrypted SMB traffic unless the 'Secure transfer required' setting is explicitly enabled. Furthermore, the claim that encryption cannot be disabled is incorrect because this setting is fully configurable, and its default value is disabled. Therefore, additional configuration is required to enforce encrypted connections.
Trap 2: Configure a network security group (NSG) rule to block SMB traffic…
An NSG filters traffic based on network-layer attributes such as source/destination IP address, port, and protocol; it has no visibility into the SMB session's encryption state because both encrypted and unencrypted SMB traffic use TCP port 445. A rule blocking port 445 would therefore block all SMB access, including legitimate encrypted connections, rather than selectively blocking only those that lack encryption. Encryption enforcement for Azure Files must be handled at the storage/application layer, not by network security groups.
Trap 3: Set the Azure Files share to use the 'Premium' performance tier;…
The premium performance tier is related to storage throughput and latency, and it does enable customer-managed keys (CMK) for Azure Files encryption at rest, but it does not control encryption in transit. SMB encryption enforcement via the 'Secure transfer required' setting is available on both standard and premium file shares, so selecting premium is neither necessary nor sufficient to force SMB 3.0 encryption. The misconception arises from conflating at-rest encryption with in-transit SMB encryption.
- A
No additional configuration is needed; Azure Files uses SMB encryption by default and cannot be disabled.
Why wrong: Azure Files does support SMB 3.0 encryption, but the protocol version and encryption are not mandatory by default; the storage account will accept unencrypted SMB traffic unless the 'Secure transfer required' setting is explicitly enabled. Furthermore, the claim that encryption cannot be disabled is incorrect because this setting is fully configurable, and its default value is disabled. Therefore, additional configuration is required to enforce encrypted connections.
- B
Enable 'Secure transfer required' in the storage account's configuration to enforce SMB 3.0 encryption.
Enabling 'Secure transfer required' on the storage account is the correct control because it rejects all insecure connections, including HTTP and SMB sessions that do not use encryption. For Azure Files, this forces clients to negotiate SMB 3.0 with encryption (or SMB 3.1.1), as older SMB versions are disallowed. This setting applies at the storage account level and covers all file shares within it, ensuring that every SMB client connection is encrypted.
- C
Configure a network security group (NSG) rule to block SMB traffic on port 445 that does not use encryption.
Why wrong: An NSG filters traffic based on network-layer attributes such as source/destination IP address, port, and protocol; it has no visibility into the SMB session's encryption state because both encrypted and unencrypted SMB traffic use TCP port 445. A rule blocking port 445 would therefore block all SMB access, including legitimate encrypted connections, rather than selectively blocking only those that lack encryption. Encryption enforcement for Azure Files must be handled at the storage/application layer, not by network security groups.
- D
Set the Azure Files share to use the 'Premium' performance tier; encryption is only available on premium shares.
Why wrong: The premium performance tier is related to storage throughput and latency, and it does enable customer-managed keys (CMK) for Azure Files encryption at rest, but it does not control encryption in transit. SMB encryption enforcement via the 'Secure transfer required' setting is available on both standard and premium file shares, so selecting premium is neither necessary nor sufficient to force SMB 3.0 encryption. The misconception arises from conflating at-rest encryption with in-transit SMB encryption.