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Introduction:
For years, Azure Files SMB shares lacked native Entra ID permission management, forcing organizations to maintain hybrid AD DS environments or rely on shared key access – a major blocker for cloud‑native adoption. Microsoft has finally removed this obstacle: Entra ID Kerberos authentication for cloud‑only identities is now in public preview, and managed identity support for Azure Files SMB is generally available. This enables true identity‑driven file share access without any on‑premises domain controllers.
Learning Objectives
Understand how Entra‑only Kerberos authentication works for Azure Files SMB shares.
Learn to disable storage account key access and enforce identity‑based security.
Configure directory‑level Windows ACLs using native Entra ID permissions.
You Should Know
- The Game‑Changing Capability: Entra‑Only Kerberos Authentication for Azure Files SMB
Historically, enabling identity‑based access to Azure file shares required Active Directory Domain Services (AD DS) or Entra Domain Services, with identities synced from on‑premises. This was a dealbreaker for cloud‑only organizations. The new Entra‑only identity support (public preview) eliminates that dependency: cloud‑only identities can now obtain Kerberos tickets directly from Microsoft Entra ID without any domain controller .
How it works behind the scenes:
- A user with a cloud‑only identity attempts to access an Azure Files SMB share.
- The SMB client requests a Kerberos service ticket for the resource’s SPN:
cifs/<storageaccount>.file.core.windows.net. - Instead of an on‑prem KDC, Microsoft Entra ID issues the Kerberos service ticket based on the user’s cloud TGT.
- Azure Files validates the ticket and enforces share‑level RBAC permissions .
Prerequisites (cloud‑only identities):
Client device must be Entra joined or Entra hybrid joined.
Device must be able to retrieve Kerberos tickets (via Intune, Group Policy, or registry).
Supported OS: Windows 11, Windows Server 2025.
The storage account must be excluded from MFA policies (Kerberos auth doesn’t yet support interactive MFA prompts) .
⚠️ Limitation: As of preview, cloud‑only identities do not support directory or file‑level permissions (Windows ACLs) – only share‑level RBAC roles are enforced. Hybrid identities (synced from AD DS) can still use full NTFS permissions .
2. Step‑by‑Step Implementation & Hardening Guide
Step 1: Enable Microsoft Entra Kerberos authentication on your storage account
Azure Portal:
Navigate to your storage account → File shares → Identity‑based access → Select Microsoft Entra Kerberos → Enable the checkbox → Save.
Behind the scenes, a service principal is created on your tenant – you then grant admin consent to the tenant .
PowerShell / Azure CLI (alternative):
Use `Set-AzStorageAccount` with `-EnableAzureActiveDirectoryKerberos` flag (if supported).
Step 2: Disable storage account key access (critical hardening)
The most common “backdoor” is leaving storage keys enabled. As one commenter noted: “Good progress, but I still wouldn’t call it solved if storage keys stay enabled. That’s basically identity‑based access with a side door.”
To enforce true identity‑only access:
- In the storage account, go to Configuration → Allow storage account key access → Set to Disabled.
- This forces all access to go through Entra ID authentication – keys become unusable.
- Important: Ensure all clients are properly configured for Entra Kerberos before disabling keys to avoid access outages.
Step 3: Assign share‑level RBAC permissions
Use built‑in roles for Entra‑only access:
| Role | Capability |
||-|
| Storage File Data SMB Share Reader | Read file/directory metadata and list contents |
| Storage File Data SMB Share Contributor | Read, write, delete, and modify permissions (excluding NTFS ACLs) |
| Storage File Data SMB Share Elevated Contributor | Full control including NTFS permission changes |
PowerShell example:
New-AzRoleAssignment -ObjectId "<user-or-group-object-id>" ` -RoleDefinitionName "Storage File Data SMB Share Contributor" ` -Scope "/subscriptions/<sub-id>/resourceGroups/<rg>/providers/Microsoft.Storage/storageAccounts/<account>/fileShares/<share>"
Step 4: Mount the file share from a Windows device using Entra identity
Before mounting, ensure you have removed any existing credentials:
Remove cached credentials and existing connections
cmdkey /list | findstr "yourstorageaccount.file.core.windows.net" | ForEach-Object { cmdkey /del:$($_.Split()[bash]) }
net use /delete /y
Now mount the share persistently using your Entra ID credentials:
$connectTestResult = Test-NetConnection -ComputerName <storage-account>.file.core.windows.net -Port 445
if ($connectTestResult.TcpTestSucceeded) {
Mount using current Windows identity
net use Z: \<storage-account>.file.core.windows.net\<share-name> /persistent:yes
} else {
Write-Error "Port 445 is blocked – consider SMB over QUIC or VPN"
}
Step 5: Apply directory / file‑level permissions (hybrid identities only)
For hybrid identities, use `icacls` or File Explorer after mounting:
Mount with admin access (requires Storage File Data SMB Share Elevated Contributor role) net use Z: \<storage-account>.file.core.windows.net\<share-name> /persistent:yes Grant modify permission to a user on a specific folder icacls Z:\Finance /grant "domain\user:(OI)(CI)M" /T View existing permissions icacls Z:\Finance
For cloud‑only identities (preview), directory‑level NTFS permissions are not supported – only share‑level RBAC applies.
Step 6: Prepare macOS clients (Platform SSO required)
To access Entra‑authenticated Azure Files from macOS, you must configure Cloud Kerberos via Intune:
- Create a macOS Configuration Profile using Settings Catalog.
2. Add Extensible Single Sign On Kerberos settings.
3. Configure:
– `Allow Automatic Login = True`
– `Perform Kerberos Only = True`
– `Preferred KDCs = kkdcp://login.microsoftonline.com/
– `Realm = KERBEROS.MICROSOFTONLINE.COM`
– `Hosts = .windows.net, windows.net, kerberos.microsoftonline.com`
4. Assign the profile to users (not devices) and reboot .
- The Port 445 Blocking Problem – Will QUIC Save Us?
A recurring frustration highlighted in the discussion: port 445 is blocked by many ISPs and corporate firewalls. Nathan Hutchinson asked: “Do you know if it has QUIC support yet? I know port 445 is blocked by some network providers and almost certainly in a lot of orgs internal networks.”
Current reality: SMB over QUIC (UDP 443) is not yet available in Azure Files – it requires Windows Server 2022+ file servers with certificates. Today, Azure Files still relies on TCP 445.
Workarounds:
Point‑to‑site VPN into Azure VNet (encapsulates SMB traffic).
Azure File Sync (uses QUIC for sync but not direct access).
Expected future: Microsoft has indicated that QUIC support is on the roadmap, which would allow SMB traffic over UDP 443 – firewall‑friendly and TLS 1.3 encrypted without VPN .
4. Security Analysis: Attack Surface Reduction & Mitigations
Before (legacy model):
Shared keys provided unrestricted access – a leaked key meant full data exposure.
Hybrid AD DS added complexity and required domain controller maintenance.
No native MFA for SMB authentication.
After (Entra‑only + key disabled):
Every access is identity‑driven and auditable via Entra ID logs.
Conditional Access policies can restrict access based on location, device compliance, or risk.
No standing credentials – Kerberos tickets are time‑limited.
Critical hardening checklist:
1. Disable shared key access entirely after migration.
- Exclude the storage account from MFA (Kerberos limitation – monitor for GA changes).
- Use Privileged Identity Management (PIM) for Storage File Data roles.
- Enable Azure Monitor logs for SMB file access events.
- Implement network restrictions: Configure IP firewalls or private endpoints.
What Undercode Say:
- Key Takeaway 1: The removal of hybrid AD dependency is a watershed moment – cloud‑only organizations can finally use Azure Files without legacy infrastructure, though the lack of NTFS permissions for cloud identities remains a major gap.
- Key Takeaway 2: Disabling storage account keys is mandatory for true identity‑based security. Leaving keys enabled creates a silent backdoor that bypasses all Entra controls and defeats the purpose.
Analysis: This announcement fundamentally shifts the economics of file storage in Azure. Traditional on‑prem file servers can now be fully replaced by Azure Files without the overhead of domain controllers, sync services, or VPN complexities – provided port 445 can be opened. The current preview limitations (no NTFS for cloud identities, no QUIC) are temporary speed bumps. Organizations already invested in Intune and Entra joined devices will benefit immediately. However, the missing macOS support for identity‑based SMB (as of this writing) forces hybrid auth for Mac users.
Prediction:
By Q4 2026 – early 2027, we will see:
SMB over QUIC GA for Azure Files, enabling secure internet‑native file access without port 445 or VPN.
Full NTFS permission support for cloud‑only identities, closing the hybrid parity gap.
Native MFA integration with Kerberos, removing the current exemption requirement.
Azure Files becoming the default storage backend for Entra‑joined Windows devices, displacing on‑prem file servers entirely for most organizations.
The death of the traditional file server is finally here – not with a whimper, but with a Kerberos ticket.
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