The Hidden Risk in Entra ID: Why Blocking an Agent Identity in Conditional Access Fails + Video

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Introduction:

Identity Admins and Security Operations Center (SOC) analysts are increasingly focused on securing non-human identities, particularly Agent Identities within Microsoft Entra ID. These identities, used by applications and services, operate with distinct permissions and authentication flows that differ from standard user accounts. A recent deep-dive has revealed a critical and confusing gap in the remediation process: blocking an Agent Identity or its associated Blueprint in Conditional Access does not prevent the corresponding Agent User from obtaining access tokens, creating a significant blind spot in identity security strategies.

Learning Objectives:

  • Differentiate between the various Agent Identity types within Microsoft Entra ID.
  • Learn how to manually create and manage these identities using PowerShell.
  • Understand the limitations of Conditional Access policies when remediating Agent Identities.
  • Implement effective methods to block and monitor Agent Identities using Microsoft Graph and best practices.
  • Identify and mitigate risks associated with the “Agent User” token acquisition flow.

You Should Know:

1. Understanding Entra ID Agent Identity Types

Agent Identities in Entra ID are not a single entity but a combination of components that work together to grant applications and services access to resources. To effectively manage them, you must first understand the core components: the Agent Identity, the Agent Blueprint, and the Agent User.
– Agent Identity: This is the primary service principal or application registration. It holds the credentials (certificates, client secrets) and defines the core permissions required by the application.
– Agent Blueprint: This acts as a configuration template. It defines the authentication methods and settings that the Agent Identity will use to request tokens.
– Agent User: This is a user object (often a service account) that the Agent Identity can impersonate or act on behalf of. This is where the complexity and risk lie, as tokens are ultimately issued for this user context.

2. Manual Creation and Identification via PowerShell

Understanding the architecture is one thing; seeing it in your own tenant is another. As an Identity Admin, you can use PowerShell to enumerate and understand these identities. First, ensure you have the Microsoft Graph PowerShell SDK installed. This process helps you identify potential “Agent Users” that might be linked to application identities.

Step-by-step guide:

  1. Connect to Microsoft Graph: `Connect-MgGraph -Scopes “Application.Read.All”, “User.Read.All”, “Directory.Read.All”`
    2. List all Service Principals (Agent Identities): `Get-MgServicePrincipal | Select DisplayName, Id, AppId`
    3. Examine a specific Service Principal’s Owners and App Roles: This helps identify who controls the identity and what permissions it has.

    $spId = "Enter-ServicePrincipal-Id-Here"
Get-MgServicePrincipalOwner -ServicePrincipalId $spId
Get-MgServicePrincipalAppRoleAssignedTo -ServicePrincipalId $spId
  2. Identify potential Agent Users: Search for user accounts that are service accounts or have names indicating automated use (e.g., svc-, app-). Cross-reference these with the `AppRoleAssignedTo` assignments from the previous step to see if a user is directly assigned to an application role, which might indicate an “Agent User” relationship.

`Get-MgUser -Filter “startswith(displayName,’svc-‘)” -Property Id, DisplayName, UserPrincipalName`

  1. The Conditional Access Gap: Querying with Microsoft Graph
    The critical finding highlighted is that blocking the Agent Identity or Blueprint in Conditional Access does not stop the Agent User from acquiring a token. To test this gap, you can use Microsoft Graph API calls to query the conditional access policies and then attempt a token acquisition for the Agent User. This requires a tool like Postman or a PowerShell script with delegated permissions.

Step-by-step guide:

  1. Query Conditional Access Policies: Use Graph API to list all policies applied to a specific service principal.
    `GET https://graph.microsoft.com/v1.0/identity/conditionalAccess/policies?$filter=conditions/applications/includeApplications/any(a:a eq ‘appId-of-agent-identity’)`
    2. Simulate a Token Request: In a secure test environment, attempt to get a token for the Agent User using the client credentials flow of the Agent Identity. You can simulate this with PowerShell:

    $tenantId = "your-tenant-id"
$clientId = "appId-of-agent-identity"
$clientSecret = "your-client-secret"
$scope = "https://graph.microsoft.com/.default"</li>
</ol>

$body = @{
client_id = $clientId
client_secret = $clientSecret
scope = $scope
grant_type = "client_credentials"
}

Even if the Agent Identity is blocked in CA, this request may succeed
 if the token is issued for the Agent User context.
$tokenResponse = Invoke-RestMethod -Method Post -Uri "https://login.microsoftonline.com/$tenantId/oauth2/v2.0/token" -Body $body
$tokenResponse.access_token

    If this command returns an access token despite the Conditional Access block on the Agent Identity, you have confirmed the gap in your environment.

    1. Effective Remediation: Disabling and Hardening the Agent User
      Since Conditional Access fails to fully block access, the remediation strategy must target the source of the token: the Agent User account. This requires a more direct and aggressive approach.

    Step-by-step guide:

    1. Identify the Agent User: As shown in section 2, determine which user account is being used by the Agent Identity. This is often found in the application’s configuration or by reviewing sign-in logs for the service principal, which will show the user context.
    2. Disable the User Account (Immediate Action): The most effective way to stop access is to disable the Agent User account in Entra ID.

    – Portal: Azure AD > Users > Select the user > Edit > Block sign-in > Yes.
    – PowerShell: `Update-MgUser -UserId “[email protected]” -AccountEnabled:$false`
    3. Reset the Password/Revoke Tokens: After disabling, immediately reset the user’s password and revoke all existing sessions and refresh tokens.
    – PowerShell: `Revoke-MgUserSignInSession -UserId “[email protected]”`

    5. Proactive Monitoring and Alerting

    To prevent future incidents, SOC teams must set up monitoring to detect anomalous behavior from Agent Identities and their associated users. This shifts the focus from a reactive block to proactive detection.

    Step-by-step guide:

    1. Enable Diagnostic Settings for Sign-in Logs: Stream sign-in logs to a Log Analytics workspace or a SIEM.
    2. Create KQL Queries for Anomalies: Use the following query in Log Analytics to detect sign-ins from an Agent User that occur outside of business hours or from unexpected locations, especially when the sign-in is tied to an application. 
      SigninLogs
| where UserPrincipalName contains "svc-" or UserPrincipalName contains "agent"
| where ResultType == 0
| extend Location = strcat(tostring(LocationDetails.countryOrRegion), "/", tostring(LocationDetails.city))
| where TimeGenerated between (datetime(yyyy-mm-ddThh:mm:ssZ) .. datetime(yyyy-mm-ddThh:mm:ssZ)) // Adjust time window
| project TimeGenerated, UserPrincipalName, AppDisplayName, IPAddress, Location
    3. Set Up Alerts: Convert these queries into Azure Monitor alerts. Configure an action group to notify the SOC team via email, SMS, or a ticketing system whenever a suspicious sign-in by an Agent User is detected.

    What Undercode Say:

    • Key Takeaway 1: The “Agent User” is the ultimate source of privilege. Remediation efforts that focus solely on the application’s service principal or Conditional Access policies are incomplete and will fail to secure your environment. You must treat the linked user account with the same rigor as a privileged admin account.
    • Key Takeaway 2: Microsoft’s classification of this as “expected behavior” highlights a fundamental architectural principle: tokens are issued to a security principal (a user), not just an application. The application is merely the client requesting the token on behalf of that principal. This requires a paradigm shift in how identity security teams view and protect non-human identities.

    Analysis:

    This gap reveals a critical vulnerability in identity security postures that have become overly reliant on Conditional Access as a catch-all control. The complexity of Entra ID’s identity model, where an application can act as a client for a user, creates a dangerous abstraction layer. Security teams often lack visibility into this “user-context” layer, leading them to apply controls to the wrong object (the app) while the real target (the user) remains active. This underscores the urgent need for unified identity threat detection and response (ITDR) strategies that correlate application activity with user account risk. It is not enough to secure the key; you must also secure the door it opens. The SOC must integrate application logs with user sign-in logs to get a complete picture of identity-based attacks, which are increasingly targeting this exact type of hybrid identity.

    Prediction:

    As identity-centric attacks continue to evolve, we will see a rise in adversaries exploiting this architectural gap. Attackers will compromise a low-privilege application’s credentials and then use the associated “Agent User” account to move laterally, as that account likely has broader access than the application itself. This will force Microsoft and other identity providers to eventually re-architect how “on-behalf-of” flows are governed, likely introducing new policy controls specifically designed to govern the relationship between an application and the user it impersonates. In the short term, expect a surge in third-party tools and custom scripts designed to provide the visibility into “Agent Users” that native tools currently lack.

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