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1.4 Review Guest Users on a Regular Basis (Manual)​

Profile Applicability​

• Level 1

Description​

Azure AD includes Azure AD B2B collaboration, allowing you to invite people from outside your organization to be guest users in your cloud account and sign in with their own work, school, or social identities. Guest users allow you to share your company's applications and services with users from any other organization, while maintaining control over your own corporate data.

Work with external partners, large or small, even if they do not have Azure AD or an IT department. A simple invitation and redemption process lets partners use their own credentials to access your company's resources as a guest user.

Review guest users in every subscription on a regular basis, and remove any inactive and unneeded accounts.

Rationale​

Guest users in the Azure AD are generally required for collaboration purposes in Office 365, and may also be required for Azure functions in enterprises with multiple Azure tenants. Guest users are typically added outside your employee on-boarding/off-boarding process and could potentially be overlooked indefinitely, leading to a potential vulnerability. To prevent this, guest users should be reviewed on a regular basis. During this audit, guest users should also be determined to not have administrative privileges.

Impact​

Before removing guest users, determine their use and scope. Like removing any user, there may be unforeseen consequences to systems if it is deleted.

Audit​

From Azure Portal​

  1. From Azure Home select the Portal Menu
  2. Select Azure Active Directory
  3. Then Users and group
  4. Select All Users
  5. Click on Add filters button, select User type, click Apply, select Guest, click Apply
  6. Audit the listed guest users.

From Azure CLI​

az ad user list --query "[?userType=='Guest']"

Ensure all users listed are still required and not inactive.

From Azure Powershell​

Get-AzureADUser |Where-Object {$_.UserType -like "Guest"} |Select-Object DisplayName, UserPrincipalName, UserType -Unique

Remediation​

From Azure Portal​

  1. From Azure Home select the Portal Menu.
  2. Select Azure Active Directory.
  3. Select Users.
  4. Click Add filter.
  5. Select User type.
  6. Select Guest from the Value dropdown.
  7. Click Apply.
  8. Delete all Guest users that are no longer required or are inactive.

From Azure CLI​

Before deleting the user, set it to inactive using the ID from the Audit Procedure to determine if there are any dependent systems.

az ad user update --id <exampleaccountid@domain.com> --account-enabled {false}

After determining that there are no dependent systems delete the user:

Remove-AzureADUser -ObjectId <exampleaccountid@domain.com>

From Azure Powershell​

Before deleting the user, set it to inactive using the ID from the Audit Procedure to determine if there are any dependent systems.

Set-AzureADUser -ObjectId "<exampleaccountid@domain.com>" -AccountEnabled false

After determining that there are no dependent systems delete the user:

PS C:\>Remove-AzureADUser -ObjectId <exampleaccountid@domain.com>

References​

https://docs.microsoft.com/en-us/azure/active-directory/b2b/user-properties
https://docs.microsoft.com/en-us/azure/active-directory/fundamentals/add-users-azure-active-directory#delete-a-user
https://docs.microsoft.com/en-us/security/benchmark/azure/security-controls-v3-privileged-access#pa-3-review-and-reconcile-user-access-regularly
https://www.microsoft.com/en-us/security/business/identity-access-management/azure-ad-pricing
https://docs.microsoft.com/en-us/azure/active-directory/reports-monitoring/howto-manage-inactive-user-accounts
https://docs.microsoft.com/en-us/azure/active-directory/fundamentals/active-directory-users-restore

Additional Information​

It is good practice to use a dynamic group to manage guest users.

To create the dynamic group:

  1. Navigate to the 'Active Directory' blade in the Azure Portal.
  2. Select the 'Groups' item.
  3. Select 'New Group'.
  4. Type of 'dynamic'.
  5. Use the following dynamic selection rule: "(user.userType -eq "Guest")".
  6. After creation of the group, select access reviews option and create a new access review with a period of monthly and send to relevant administrators for review.
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