Cis Azure Foundations 9.1.3

Ensure 'SMB channel encryption' is set to 'AES-256-GCM' or higher for SMB file shares

Description

Implement SMB channel encryption with AES-256-GCM for SMB file shares to ensure data confidentiality and integrity in transit. This method offers strong protection against eavesdropping and man-in-the-middle attacks, safeguarding sensitive information.

Rationale

AES-256-GCM encryption enhances the security of data transmitted over SMB channels by safeguarding it from unauthorized interception and tampering.

Impact

Using the AES-256-GCM SMB channel encryption may impact client compatibility.

Audit Procedure

Audit from Azure Portal

1. Go to Storage accounts.
2. Click the name of a storage account.
3. Under Data storage, click File shares.
4. Under File share settings, click the link next to Security.
5. Under SMB channel encryption, ensure that AES-256-GCM, or higher, is the only checked SMB channel encryption setting.
6. Repeat steps 1-5 for each storage account.

Audit from Azure CLI

Run the following command to list storage accounts:

az storage account list

For each storage account, run the following command:

az storage account file-service-properties show --resource-group <resource-group> --account-name <storage-account>

Ensure that under protocolSettings > smb, channelEncryption is set to AES-256-GCM;, or higher, only.

Audit from PowerShell

Run the following command to list storage accounts:

Get-AzStorageAccount

Run the following command to get the file service properties for a storage account in a resource group with a given name:

$storageaccountfileservice = Get-AzStorageFileServiceProperty -ResourceGroupName <resource-group> -AccountName <storage-account>

Run the following command to get the SMB channel encryption setting:

$storageaccountfileservice.ProtocolSettings.Smb.ChannelEncryption

Ensure that the command returns AES-256-GCM, or higher, only.

Expected Result

SMB channel encryption should be set to AES-256-GCM or higher only.

Remediation

Remediate from Azure Portal

1. Go to Storage accounts.
2. Click the name of a storage account.
3. Under Data storage, click File shares.
4. Under File share settings, click the link next to Security.
5. If Profile is set to Maximum compatibility, click the drop-down menu and select Maximum security or Custom.
6. If selecting Custom, under SMB channel encryption, uncheck the boxes next to AES-128-CCM and AES-128-GCM.
7. Click Save.
8. Repeat steps 1-7 for each storage account requiring remediation.

Remediate from Azure CLI

For each storage account requiring remediation, run the following command to set the SMB channel encryption:

az storage account file-service-properties update --resource-group <resource-group> --account-name <storage-account> --channel-encryption AES-256-GCM

Remediate from PowerShell

For each storage account requiring remediation, run the following command to set the SMB channel encryption:

Update-AzStorageFileServiceProperty -ResourceGroupName <resource-group> -StorageAccountName <storage-account> -SmbChannelEncryption AES-256-GCM

Default Value

By default, the following SMB channel encryption algorithms are allowed: AES-128-CCM, AES-128-GCM, and AES-256-GCM.

References

1. https://learn.microsoft.com/en-us/azure/well-architected/service-guides/azure-files#recommendations-for-smb-file-shares
2. https://learn.microsoft.com/en-us/azure/storage/files/files-smb-protocol#smb-security-settings
3. https://learn.microsoft.com/en-us/cli/azure/storage/account/file-service-properties
4. https://learn.microsoft.com/en-us/powershell/module/az.storage/get-azstoragefileserviceproperty
5. https://learn.microsoft.com/en-us/powershell/module/az.storage/update-azstoragefileserviceproperty

Profile

Level 1