How to Exploit Azure AD Sign-in Data to Detect Problem Service Principals

Spring Clean Time for Apps Coming Soon

Last year, I wrote about the need to review and clean up Azure AD integrated applications. That article describes how to extract information from Azure AD to a CSV file and use the CSV to create a Microsoft List. To make it easy to access the list, we create a channel tab in Teams. Everything works to identify suspect apps that might need removal. I think that you should perform such a review periodically. It just makes sense.

Another way to monitor potentially suspicious app activity is to review sign in data for service principals. The intention is to identify unrecognized service principals signing into the tenant and figure out what apps are involved. Sign-ins can originate from well-known service principals used by Microsoft apps, third-party apps, or the service principals automatically created by Azure AD when tenants register apps to interact with the Graph (for instance, to authenticate calls made to Graph APIs in PowerShell scripts). Sign-in data for service principals is available through the Azure AD admin center (Figure 1) and now it’s accessible using the Microsoft Graph List SignIns API.

Sign-in logs for service principals in the Azure AD admin center
Figure 1: Sign-in logs for service principals in the Azure AD admin center

The reason why this update is important is that access to sign-in data via the Graph makes it possible to download the information for analysis or store it for long-term retention in an external repository. Although you can download sign-in data as a CSV file the Azure AD admin center, it’s more flexible to access the information via Graph queries, especially when you want to probe the activity patterns of certain service principals.

Getting Sign-In Data from the Graph

Any application which wants to interact with the Graph requires consent for permissions to access data. In this instance, consent is needed the Directory.Read.All and AuditLog.Read.All application permissions. Delegate permissions can also be used, and in this case the account used must hold an administrative role capable of accessing the Azure AD sign-in logs.

A suitably-permissioned application can issue queries against the SignIns API. To fetch service principal sign-in data, the query executed by the application must use a Lambda qualifier to filter data. Apart from setting a date range to search for sign-in data, the important point is to filter against the signInEventTypes property to select sign-in events for service principals. Here’s an example of a query to fetch sign-in data for between 17:30 and 22:3 on 19 January.$filter=createdDateTime ge 2022-01-19T17:30:00Z and createdDateTime le 2022-01-19T22:30:00Z and signInEventTypes/any(x:x eq 'servicePrincipal')

To test the query (or one which suits your purposes), use the Graph Explorer to see what the query returns.

I wrote a simple PowerShell script (downloadable from GitHub) to fetch service principal sign-in data for the last seven days. A quick summary of the data revealed that many sign-ins came from an app named Office 365 Reports. Curiously, an app used by a PowerShell script that I had posted on GitHub also showed up with 22 sign-ins. The Information Barrier Processor is the app used by Microsoft 365 to check user accounts against information barrier policies to ensure that no one is communicating with anyone when they shouldn’t.

$Report | Group SpName | Sort Count -Descending | Select Name, Count

Name                                         Count
----                                         -----
Office 365 Reports                             369
Graph Microsoft 365 Groups Membership Report    22
Information Barrier Processor                   21
Security and Audit                               5
PS-Graph                                         1

Resolving the large set of sign-ins was easy. The data stored in the list (Figure 2) revealed the service principal to belong to an Office 365 Reporting app originally published by Cogmotive (acquired by Quadrotech and then by Quest Software). I haven’t used the app in years, but the sign-ins kept on coming.

Service Principal information
Figure 2: Service Principal information

Over time, it’s easy to accumulate crud in the form of service principals installed for one reason or another. Testing an ISV product is a classic example, which is a good reason to always conduct tests in a test tenant instead of the production tenant. Or if you stop using an app, remember to clean up by removing service principals and other app debris that the app vendor might leave behind.

The sign-ins for the app used by the PowerShell script probably exist because I shared a copy of the script with my tenant identifier, the app identifier, and the app secret in place. I quickly replaced the script with a copy containing obfuscated credentials, but failed to change the app secret, meaning that anyone with an original copy could run the code. Now alerted, I removed the app secret. My suspicions were confirmed when a batch of failed sign-ins subsequently occurred for the app. This goes to prove how easy it is to create a potential compromise if you’re not careful.

Removing a Service Principal with PowerShell

You can clean up unwanted service principals with either the Azure AD admin center or PowerShell. I always have a PowerShell session open, so I chose that route. In this example, we find the object identifier for a service principal using its display name. When sure that this is the right service principal to remove, we use the object identifier to remove the service principal with the Remove-AzureADServicePrincipal cmdlet.

Get-AzureADServicePrincipal -SearchString "Office 365 Reports"

ObjectId                             AppId                                DisplayName
--------                             -----                                -----------
034b71f3-f57a-4bed-84b9-07207ee5998e 507bc9da-c4e2-40cb-96a7-ac90df92685c Office 365 Reports

$AppId = (Get-AzureADServicePrincipal -SearchString "Office 365 Reports").ObjectId
Remove-AzureADServicePrincipal -ObjectId $AppId

Adding Context

A list of service principals known to the tenant is a valuable input to a review for unwanted or unnecessary apps holding some form of consent (permissions) to organization data. Adding context to the data by knowing which service principals are actively signing into the tenant makes it easier to prioritize action. The data is there, it’s available, and it’s up to you to decide what to do with it.

Insight like this doesn’t come easily. You’ve got to know the technology and understand how to look behind the scenes. Benefit from the knowledge and experience of the Office 365 for IT Pros team by subscribing to the best eBook covering Office 365 and the wider Microsoft 365 ecosystem.

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