Control: 1.1.6 Enable Conditional Access policies to block legacy authentication

Description

Use Conditional Access to block legacy authentication protocols in Office 365.

Legacy authentication protocols do not support multi-factor authentication. These protocols are often used by attackers because of this deficiency. Blocking legacy uthentication makes it harder for attackers to gain access.

Remediation

To setup a conditional access policy to block legacy authentication, use the following steps:

Log in to https://admin.microsoft.com as a Global Administrator.
Go to Admin centers and click on Azure Active Directory.
Select Azure Active Directory then Security.
Select Conditional Access.
Create a new policy by selecting New policy.
Set the following conditions within the policy.
- Select Conditions then Client apps enable the settings for and Exchange ActiveSync clients and other clients.
- Under Access controls set the Grant section to Block access.
- Under Assignments enable All users.
- Under Assignments and Users and groups set the Exclude to be at least one low risk account or directory role. This is required as a best practice.

Default Value: Legacy authentication is enabled by default.

Note: For more granularity the following Audit/Remediation procedure could be utilized.

To disable basic authentication, use the Exchange Online PowerShell Module:

Run the Microsoft Exchange Online PowerShell Module.
Connect using Connect-ExchangeOnline.
Run the following PowerShell command:

Note: If a policy exists and a command fails you may run Remove-AuthenticationPolicy first to ensure policy creation/application occurs as expected.

$AuthenticationPolicy = Get-OrganizationConfig | Select-Object DefaultAuthenticationPolicy

If (-not $AuthenticationPolicy.Identity) { $AuthenticationPolicy = New-AuthenticationPolicy "Block Basic Auth" Set-OrganizationConfig -DefaultAuthenticationPolicy $AuthenticationPolicy.Identity }

Set-AuthenticationPolicy -Identity $AuthenticationPolicy.Identity - AllowBasicAuthActiveSync:$false -AllowBasicAuthAutodiscover:$false - AllowBasicAuthImap:$false -AllowBasicAuthMapi:$false - AllowBasicAuthOfflineAddressBook:$false -AllowBasicAuthOutlookService:$false -AllowBasicAuthPop:$false -AllowBasicAuthPowershell:$false - AllowBasicAuthReportingWebServices:$false -AllowBasicAuthRpc:$false -
AllowBasicAuthSmtp:$false -AllowBasicAuthWebServices:$false

Get-User -ResultSize Unlimited | ForEach-Object { Set-User -Identity $_.Identity -AuthenticationPolicy $AuthenticationPolicy.Identity - STSRefreshTokensValidFrom $([System.DateTime]::UtcNow) }

Usage

Run the control in your terminal:

powerpipe control run microsoft365_compliance.control.cis_v140_1_1_6

Snapshot and share results via Turbot Pipes:

powerpipe login
powerpipe control run microsoft365_compliance.control.cis_v140_1_1_6 --share

SQL

This control uses a named query:

with block_legacy_authentication as (
  select
    tenant_id,
    count(*)
  from
    azuread_conditional_access_policy
  where
    client_app_types ?& array['exchangeActiveSync', 'other']
    and built_in_controls ?& array['block']
    and users -> 'includeUser' ?& array['All']
    and jsonb_array_length(users -> 'excludeUser') != 0
  group by
    tenant_id
),
tenant_list as(
  select
    distinct on(tenant_id) tenant_id,
    _ctx
  from
    azuread_user
)
select
  tenant_id as resource,
  case
    when (select count from block_legacy_authentication where tenant_id = t.tenant_id) > 0 then 'ok'
    else 'alarm'
  end as status,
  case
    when (select count from block_legacy_authentication where tenant_id = t.tenant_id) > 0 then tenant_id || ' has Conditional Access policies enabled.'
    else tenant_id || ' has Conditional Access policies disabled.'
  end as reason
  , t.tenant_id as tenant_id
from
  tenant_list as t;

Control: 1.1.6 Enable Conditional Access policies to block legacy authentication

Description

Remediation

Usage

SQL

Tags