Cis Azure Foundations 9.1.2

Ensure 'SMB protocol version' is set to 'SMB 3.1.1' or higher for SMB file shares

Description

Ensure that SMB file shares are configured to use the latest supported SMB protocol version. Keeping the SMB protocol updated helps mitigate risks associated with older SMB versions, which may contain vulnerabilities and lack essential security controls.

Rationale

Using the latest supported SMB protocol version enhances the security of SMB file shares by preventing the exploitation of known vulnerabilities in outdated SMB versions.

Impact

Using the latest SMB protocol version 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 protocol versions, ensure that SMB3.1.1 is the only checked protocol version.
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, versions is set to SMB3.1.1; 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 protocol version setting:

$storageaccountfileservice.ProtocolSettings.Smb.Versions

Ensure that the command returns SMB3.1.1 only.

Expected Result

SMB protocol versions should be set to SMB3.1.1 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 protocol versions, uncheck the boxes next to SMB 2.1 and SMB 3.0.
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 protocol version:

az storage account file-service-properties update --resource-group <resource-group> --account-name <storage-account> --versions SMB3.1.1

Remediate from PowerShell

For each storage account requiring remediation, run the following command to set the SMB protocol version:

Update-AzStorageFileServiceProperty -ResourceGroupName <resource-group> -StorageAccountName <storage-account> -SmbProtocolVersion SMB3.1.1

Default Value

By default, all SMB versions are allowed.

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