Cis Azure Foundations 5.15

Ensure 'Guest users access restrictions' is set to 'Guest user access is restricted to properties and memberships of their own directory objects'

Description

Limit guest user permissions.

Rationale

Limiting guest access ensures that guest accounts do not have permission for certain directory tasks, such as enumerating users, groups or other directory resources, and cannot be assigned to administrative roles in your directory. Guest access has three levels of restriction:

1. Guest users have the same access as members (most inclusive),
2. Guest users have limited access to properties and memberships of directory objects (default value),
3. Guest user access is restricted to properties and memberships of their own directory objects (most restrictive).

The recommended option is the 3rd, most restrictive: "Guest user access is restricted to their own directory object".

Impact

This may create additional requests for permissions to access resources that administrators will need to approve. Some services (Forms, Project, Yammer, Planner in SharePoint) without current support might have compatibility issues with the new guest restriction setting.

Audit Procedure

Using Azure Portal

1. From Azure Home select the Portal Menu
2. Select Microsoft Entra ID
3. Under Manage, select External Identities
4. Select External collaboration settings
5. Under Guest user access, ensure that Guest user access restrictions is set to Guest user access is restricted to properties and memberships of their own directory objects

Using PowerShell

Connect-MgGraph
(Get-MgPolicyAuthorizationPolicy).GuestUserRoleId

If the GuestUserRoleId property does not equal 2af84b1e-32c8-42b7-82bc-daa82404023b then it is not set to most restrictive.

Expected Result

Guest user access restrictions should be set to Guest user access is restricted to properties and memberships of their own directory objects. The GuestUserRoleId should equal 2af84b1e-32c8-42b7-82bc-daa82404023b.

Remediation

Using Azure Portal

1. From Azure Home select the Portal Menu
2. Select Microsoft Entra ID
3. Under Manage, select External Identities
4. Select External collaboration settings
5. Under Guest user access, set Guest user access restrictions to Guest user access is restricted to properties and memberships of their own directory objects
6. Click Save

Using PowerShell

Update-MgPolicyAuthorizationPolicy -GuestUserRoleId "2af84b1e-32c8-42b7-82bc-daa82404023b"

Verify by running:

(Get-MgPolicyAuthorizationPolicy).GuestUserRoleId

Ensure that the GuestUserRoleId is equal to 2af84b1e-32c8-42b7-82bc-daa82404023b.

Default Value

By default, Guest users access restrictions is set to Guest users have limited access to properties and memberships of directory objects.

References

1. https://learn.microsoft.com/en-us/entra/fundamentals/users-default-permissions#member-and-guest-users
2. https://learn.microsoft.com/en-us/security/benchmark/azure/mcsb-privileged-access#pa-3-manage-lifecycle-of-identities-and-entitlements
3. https://learn.microsoft.com/en-us/security/benchmark/azure/mcsb-governance-strategy#gs-2-define-and-implement-enterprise-segmentationseparation-of-duties-strategy
4. https://learn.microsoft.com/en-us/security/benchmark/azure/mcsb-governance-strategy#gs-6-define-and-implement-identity-and-privileged-access-strategy
5. https://learn.microsoft.com/en-us/entra/identity/users/users-restrict-guest-permissions

CIS Controls

Profile

Level 1 | Automated