Finding Azure AD Guest Accounts in Microsoft 365 Groups

The article explaining how to report old guest accounts and their membership of Microsoft 365 Groups (and teams) in a tenant is very popular and many people use its accompanying script. The idea is to find guest accounts above a certain age (365 days – configurable in the script) and report the groups these guests are members of. Any old guest accounts that aren’t in any groups are candidates for removal.

The script uses an old technique featuring the distinguished name of guest accounts to scan for group memberships using the Get-Recipient cmdlet. The approach works, but the variation of values that can exist in distinguished names due to the inclusion of characters like apostrophes and vertical lines means that some special processing is needed to make sure that lookups work. Achieving consistency in distinguished names might be one of the reasons for Microsoft’s plan to make Exchange Online mailbox identification more effective.

In any case, time moves on and code degrades. I wanted to investigate how to use the Microsoft Graph PowerShell SDK to replace Get-Recipient. The script already uses the SDK to find Azure AD guest accounts with the Get-MgUser cmdlet.

The Graph Foundation

Graph APIs provide the foundation for all SDK cmdlets. Graph APIs provide the foundation for all SDK cmdlets. The first thing to find is an appropriate API to find group membership. I started off with getMemberGroups. The PowerShell example for the API suggests that the Get-MgDirectoryObjectMemberGroup cmdlet is the one to use. For example:

$UserId = (Get-MgUser -UserId Terry.Hegarty@Office365itpros.com).id 
[array]$Groups = Get-MgDirectoryObjectMemberGroup  -DirectoryObjectId $UserId -SecurityEnabledOnly:$False

The cmdlet works and returns a list of group identifiers that can be used to retrieve information about the groups that the user belongs to. For example:

Get-MgGroup -GroupId $Groups[0] | Format-Table DisplayName, Id, GroupTypes

DisplayName                     Id                                   GroupTypes
-----------                     --                                   ----------
All Tenant Member User Accounts 05ecf033-b39a-422c-8d30-0605965e29da {DynamicMembership, Unified}

However, because Get-MgDirectoryObjectMemberGroup returns a simple list of group identifiers, the developer must do extra work to call Get-MgGroup for each group to retrieve group properties. Not only is this extra work, calling Get-MgGroup repeatedly becomes very inefficient as the number of guests and their membership in groups increase.

Looking Behind the Scenes with Graph X-Ray

The Azure AD admin center (and the Entra admin center) both list the groups that user accounts (tenant and guests) belong to. Performance is snappy and it seemed unlikely that the code used was making multiple calls to retrieve the properties for each group. Many of the sections in these admin centers use Graph API requests to fetch information, and the Graph X-Ray tool reveals those requests. Looking at the output, it’s interesting to see that the admin center uses the beta Graph endpoint with the groups memberOf API (Figure 1).

We can reuse the call used by the Azure AD center to create the query (containing the object identifier for the user account) and run the query using the SDK Invoke-MgGraphRequest cmdlet. One change made to the command is to include a filter to select only Microsoft 365 groups. If you omit the filter, the Graph returns all the groups a user belongs to, including security groups and distribution lists. The group information is in an array that’s in the Value property returned by the Graph request. For convenience, we put the data into a separate array.

$Uri = ("https://graph.microsoft.com/beta/users/{0}/memberOf/microsoft.graph.group?`$filter=groupTypes/any(a:a eq 'unified')&`$top=200&$`orderby=displayName&`$count=true" -f $Guest.Id)
[array]$Data = Invoke-MgGraphRequest -Uri $Uri
[array]$GuestGroups = $Data.Value

Using the Get-MgUserMemberOf Cmdlet

The equivalent SDK cmdlet is Get-MgUserMemberOf. To return the set of groups an account belongs to, the command is:

[array]$Data = Get-MgUserMemberOf -UserId $Guest.Id -All
[array]$GuestGroups = $Data.AdditionalProperties

The format of returned data marks a big difference between the SDK cmdlet and the Graph API request. The cmdlet returns group information in a hash table in the AdditionalProperties array while the Graph API request returns a simple array called Value. To retrieve group properties from the hash table, we must enumerate through its values. For instance, to return the names of the Microsoft 365 groups in the hash table, we do something like this:

[Array]$GroupNames = $Null
ForEach ($Item in $GuestGroups.GetEnumerator() ) {
   If ($Item.groupTypes -eq "unified") { $GroupNames+= $Item.displayName }
}
$GroupNames= $GroupNames -join ", "

SDK cmdlets can be inconsistent in how they return data. It’s just one of the charms of working with cmdlets that are automatically generated from code. Hopefully, Microsoft will do a better job of ironing out inconsistencies when they release V2.0 of the SDK sometime later in 2023.

A Get-MgUserTransitiveMemberOf cmdlet is also available to return the membership of nested groups. We don’t need to do this because we’re only interested in Microsoft 365 groups, which don’t support nesting. The cmdlet works in much the same way:

[array]$TransitiveData = Get-MgUserTransitiveMemberOf -UserId Kim.Akers@office365itpros.com -All

The Script Based on the SDK

Because of the extra complexity in accessing group properties, I decided to use a modified version of the Graph API request from the Azure AD admin center. It’s executed using the Invoke-MgGraphRequest cmdlet, so I think the decision is justified.

When revising the script, I made some other improvements, including adding a basic assessment of whether a guest account is stale or very stale. The assessment is intended to highlight if I should consider removing these accounts because they’re obviously not being used. Figure 2 shows the output of the report.

You can download a copy of the script from GitHub.

Cleaning up Obsolete Azure AD Guest Accounts

Reporting obsolete Azure AD guest accounts is nice. Cleaning up old junk from Azure AD is even better. The script generates a PowerShell list with details of all guests over a certain age and the groups they belong to. To generate a list of the very stale guest accounts, filter the list:

[array]$DeleteAccounts = $Report | Where-Object {$_.StaleNess -eq "Very Stale"}

To complete the job and remove the obsolete guest accounts, a simple loop to call Remove-MgUser to process each account:

ForEach ($Account in $DeleteAccounts) {
   Write-Host ("Removing guest account for {0} with UPN {1}" -f $Account.Name, $Account.UPN) 
   Remove-MgUser -UserId $Account.Id }

Obsolete or stale guest accounts are not harmful, but their presence slows down processing like PowerShell scripts. For that reason, it’s a good idea to clean out unwanted guests periodically.

Learn about mastering the Microsoft Graph PowerShell SDK and the Microsoft 365 PowerShell modules by subscribing to the Office 365 for IT Pros eBook. Use our experience to understand what’s important and how best to protect your tenant.