FindOldGuestUsers.ps1

# FindOldGuestUsers.PS1
# Script to find Guest User Accounts in an Office 365 Tenant that are older than 365 days (update the $GuestAccountAge variable to set a different
# number of days to check for) and the groups they belong to
# Script needs to connect to the Microsoft Graph PowerShell SDK Exchange Online PowerShell.
# https://github.com/12Knocksinna/Office365itpros/blob/master/FindOldGuestUsers.ps1
# V2.0 10-Oct-2022

# Make sure the right modules are loaded...
If ("ExchangeOnlineManagement" -notin  $Modules.Name) {Write-Host "Please connect to Exchange Online Management  before continuing...";break}
Connect-MgGraph -Scopes AuditLog.Read.All, Directory.Read.All
Select-MgProfile Beta

# Set age threshold for reporting a guest account
[int]$AgeThreshold = 365
# Output report name
$OutputReport = "c:\Temp\OldGuestAccounts.csv"
# Get all guest accounts in the tenant
Write-Host "Finding Guest Accounts..."
[Array]$GuestUsers = Get-MgUser -Filter "userType eq 'Guest'" -All -Property signInActivity 
$Today = (Get-Date); $i = 0; $StaleGuests = 0; $Report = [System.Collections.Generic.List[Object]]::new()
# Loop through the guest accounts looking for old accounts 
CLS
ForEach ($Guest in $GuestUsers) {
# Check the age of the guest account, and if it's over the threshold for days, report it
   $AADAccountAge = ($Guest.RefreshTokensValidFromDateTime | New-TimeSpan).Days
   $i++
   If ($AADAccountAge -gt $AgeThreshold) {
      $ProgressBar = "Processing Guest " + $Guest.DisplayName + " " + $AAdAccountAge + " days old " +  " (" + $i + " of " + $GuestUsers.Count + ")"
      Write-Progress -Activity "Checking Guest Account Information" -Status $ProgressBar -PercentComplete ($i/$GuestUsers.Count*100)
      $StaleGuests++
      # Find what Microsoft 365 Groups the guest belongs to... if any
      $DN = (Get-Recipient -Identity $Guest.UserPrincipalName).DistinguishedName 
#    The distinguished name for some accounts might contain an apostrophe, so we need to process them in a certain way
     If ($Dn -like "*'*")  {
       $DNNew = "'" + "$($dn.Replace("'","''''"))" + "'"
       $Cmd = "Get-Recipient -Filter 'Members -eq '$DNnew'' -RecipientTypeDetails GroupMailbox | Select DisplayName, ExternalDirectoryObjectId"
       $GuestGroups = Invoke-Expression $Cmd }
     Else {
       $GuestGroups = (Get-Recipient -Filter "Members -eq '$Dn'" -RecipientTypeDetails GroupMailbox | Select DisplayName, ExternalDirectoryObjectId) }
     $GroupNames = $Null
     If ($GuestGroups -ne $Null) {
       $GroupNames = $GuestGroups.DisplayName -join ", " }

#    Find the last sign-in date for the guest account, which might indicate how active the account is
     $UserLastLogonDate = $Null
     $UserObjectId = $Guest.ObjectId
     $UserLastLogonDate = $Guest.SignInActivity.LastSignInDateTime
     If ($UserLastLogonDate -ne $Null) {
        $UserLastLogonDate = Get-Date ($UserLastLogonDate) -format g }
     Else {
        $UserLastLogonDate = "No recent sign in records found" }

     $ReportLine = [PSCustomObject][Ordered]@{
           UPN               = $Guest.UserPrincipalName
           Name              = $Guest.DisplayName
           Age               = $AADAccountAge
           "Account created" = $Guest.RefreshTokensValidFromDateTime  
           "Last sign in"    = $UserLastLogonDate 
           Groups            = $GroupNames
           DN                = $DN}         
     $Report.Add($ReportLine) }
}

$Report | Sort Name | Export-CSV -NoTypeInformation $OutputReport
$PercentStale = ($StaleGuests/$GuestUsers.Count).toString("P")
Write-Host ("Script complete. {0} guest accounts found aged over {1} days ({2} of total). Output CSV file is in {3}" -f $StaleGuests, $AgeThreshold, $PercentStale, $OutputReport)

# An example script used to illustrate a concept. More information about the topic can be found in the Office 365 for IT Pros eBook https://gum.co/O365IT/
# and/or a relevant article on https://office365itpros.com or https://www.practical365.com. See our post about the Office 365 for IT Pros repository # https://office365itpros.com/office-365-github-repository/ for information about the scripts we write.

# Do not use our scripts in production until you are satisfied that the code meets the need of your organization. Never run any code downloaded from the Internet without
# first validating the code in a non-production environment.