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Forestall

AZ_RDP

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Summary
Forestall ACL Alias AZ_RDP
Azure Alias Virtual Machine User Login / RDP with Entra ID
Affected Object Types Windows Virtual Machines
Exploitation Certainty Certain
Azure RBAC Roles Virtual Machine User Login (fb879df8-f326-4884-b1cf-06f3ad86be52), Virtual Machine Administrator Login (1c0163c0-47e6-4577-8991-ea5c82e286e4)

Custom Role Data Actions:

  • Microsoft.Compute/virtualMachines/login/action
  • Microsoft.Compute/virtualMachines/loginAsAdmin/action

Filter: Windows VMs with the AADLoginForWindows extension and a system-assigned managed identity

Description

AZ_RDP represents the ability to RDP into Windows Azure VMs using Microsoft Entra ID credentials. This is a data-plane permission that enables interactive desktop access without requiring local VM credentials.

Prerequisites for this edge:

  • The VM must have the AADLoginForWindows extension installed.
  • The VM must have a system-assigned managed identity enabled.
  • The principal must have Virtual Machine User Login (standard user) or Virtual Machine Administrator Login (local admin) role.
Role Access Level
Virtual Machine User Login Remote Desktop Users group
Virtual Machine Administrator Login Local Administrators group

This edge is distinct from:

  • AZ_EXECUTE_COMMAND - Uses RunCommand API, no interactive session.
  • AZ_VM_ADMIN_LOGIN - Broader scope including SSH to Linux.

Identification

PowerShell (Az Module)

Connect-AzAccount


# List Virtual Machine User Login assignments
Get-AzRoleAssignment -RoleDefinitionName "Virtual Machine User Login" |
    Select-Object DisplayName, SignInName, ObjectType, Scope |
    Format-Table -AutoSize


# List Virtual Machine Administrator Login assignments
Get-AzRoleAssignment -RoleDefinitionName "Virtual Machine Administrator Login" |
    Select-Object DisplayName, SignInName, ObjectType, Scope |
    Format-Table -AutoSize


# Find Windows VMs with the Microsoft Entra login extension
Get-AzVM | ForEach-Object {
    $extensions = Get-AzVMExtension -ResourceGroupName $_.ResourceGroupName -VMName $_.Name
    $aadExt = $extensions | Where-Object { $_.Name -eq "AADLoginForWindows" }
    if ($aadExt) {
        [PSCustomObject]@{
            VMName = $_.Name
            ResourceGroup = $_.ResourceGroupName
            OSType = $_.StorageProfile.OsDisk.OsType
            AADExtension = $aadExt.Name
            Identity = $_.Identity.Type
        }
    }
} | Format-Table -AutoSize

Exploitation

RDP with Entra ID Credentials

Method 1: RDP File Configuration (Legacy - Disables NLA)

Standard RDP connection with Entra credentials requires modifying an RDP file. This method disables Network Level Authentication (NLA).

  1. Open Remote Desktop Connection (mstsc.exe).
  2. Enter the VM’s IP address or hostname.
  3. Click Show Options -> Save As to save the .rdp file locally.
  4. Open the saved .rdp file in Notepad.
  5. Add the following lines at the bottom:
enablecredsspsupport:i:0
authentication level:i:2
  1. Save the file and double-click to connect.
  2. Enter credentials in format: .\AzureAD\[email protected]

Note: The leading .\ before AzureAD\ prevents caching issues when the VM auto-locks and you need to sign back in. Without it, you may need to re-enter AzureAD\ each time.

Method 2: Modern Entra Authentication (Keeps NLA Enabled)

For Windows 10 1809+ and Azure VMs, use modern Entra authentication which maintains NLA security:

  1. Save an RDP file as described above.
  2. Add the following lines instead:
enablerdsaadauth:i:1
targetisaadjoined:i:1
  1. Important: You must connect using the VM’s hostname (not IP address). The hostname must:
    • Match the computer name registered in Entra ID.
    • Be resolvable via DNS or local hosts file.
  2. Connect using your UPN: [email protected]

Alternatively, in mstsc.exe:

  1. Click Show Options -> Advanced tab.
  2. Check Use a web account to sign in to the remote computer.

This method triggers a modern authentication prompt supporting MFA and Conditional Access policies.

Configure an RDP file in VS Code RDP login using mstsc

Post-Exploitation - Standard User

With Virtual Machine User Login (Remote Desktop Users):

# Access managed identity token
$response = Invoke-RestMethod -Uri "http://169.254.169.254/metadata/identity/oauth2/token?api-version=2018-02-01&resource=https://management.azure.com/" -Headers @{Metadata="true"}
$response.access_token
Access managed identity token powershell

Access managed identity token powershell

Post-Exploitation - Administrator

With Virtual Machine Administrator Login (Local Administrators):

# Steal managed identity token
$response = Invoke-RestMethod -Uri "http://169.254.169.254/metadata/identity/oauth2/token?api-version=2018-02-01&resource=https://management.azure.com/" -Headers @{Metadata="true"}
$response.access_token
Access managed identity token powershell

Access managed identity token powershell

Mitigation

  1. Minimize login role assignments

    • Remove Virtual Machine User/Administrator Login from identities that dont need interactive access.
    • Use AZ_EXECUTE_COMMAND (RunCommand) for automated tasks instead.

  2. Use Virtual Machine User Login instead of Administrator Login

    • Grant standard user access unless admin is specifically required.

  3. Restrict Microsoft Entra login extension deployment

    • Only deploy the extension on VMs that require Entra-based authentication.
    • Use Azure Policy to audit extension deployments.

  4. Network security

    • Restrict RDP (port 3389) access via NSGs.
    • Use Azure Bastion for secure access without public endpoints.
    • Enable Just-in-Time VM access.

  5. Enable endpoint protection

    • Deploy Microsoft Defender for Endpoint.
    • Enable Credential Guard on supported Windows versions.

Detection

Use the Azure Portal and Microsoft Entra admin center:

  1. In Azure Portal, open the target Windows VM.
  2. Open Activity log and filter Operation for login or loginAsAdmin.
  3. Review Microsoft.Compute/virtualMachines/login/action and Microsoft.Compute/virtualMachines/loginAsAdmin/action events.
  4. Open Microsoft Entra ID -> Sign-in logs and filter Application for Azure Windows VM Sign-In.
  5. Review User, IP address, Location, Date, and Status for unexpected RDP logins.
  6. On the VM blade, review Access control (IAM) for Virtual Machine User Login and Virtual Machine Administrator Login assignments.
  7. Open Extensions + applications and confirm whether AADLoginForWindows is present.

References

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