CIS.M365.1.3.7: Ensure 'third-party storage services' are restricted in 'Microsoft 365 on the web'


ID	`CIS.M365.1.3.7`
Severity	Medium
Suite	CIS Microsoft 365 Foundations Benchmark
Product	Microsoft 365
Feature	Organization settings
Security area	External access and sharing
Resource type	Tenant
User impact of fixing	Low
Effort to fix	Low
Benchmark	CIS Microsoft 365 Foundations Benchmark 7.0.0, `1.3.7` (L2, E3 Level 2, E5 Level 2)
Framework controls	`cis-m365:1.3.7` `nist-800-53-r5:AC-20` Use of External Systems `nist-800-53-r5:CM-7` Least Functionality
MITRE ATT&CK	T1567.002
Reads from	Microsoft Graph

What this checks and how to fix it

1.3.7 (L2) Ensure ‘third-party storage services’ are restricted in ‘Microsoft 365 on the web’

Third-party storage can be enabled for users in Microsoft 365, allowing them to store and share documents using services such as Dropbox, alongside OneDrive and team sites.

Ensure Microsoft 365 on the web third-party storage services are restricted.

Rationale

By using external storage services an organization may increase the risk of data breaches and unauthorized access to confidential information. Additionally, third-party services may not adhere to the same security standards as the organization, making it difficult to maintain data privacy and security.

Impact

Impact associated with this change is highly dependent upon current practices in the tenant. If users do not use other storage providers, then minimal impact is likely. However, if users do regularly utilize providers outside of the tenant this will affect their ability to continue to do so.

Remediation action:

Navigate to Microsoft 365 admin center
Go to Settings > Org Settings > Services > Microsoft 365 on the web
Uncheck Let users open files stored in third-party storage services in Microsoft 365 on the web

PowerShell

Connect to Microsoft Graph using Connect-MgGraph -Scopes "Application.ReadWrite.All"
Run the following script:

$SP = Get-MgServicePrincipal -Filter "appId eq 'c1f33bc0-bdb4-4248-ba9b-096807ddb43e'"
# If the service principal doesn't exist then create it first.
if (-not $SP) {
    $SP = New-MgServicePrincipal -AppId "c1f33bc0-bdb4-4248-ba9b-096807ddb43e"
}
Update-MgServicePrincipal -ServicePrincipalId $SP.Id -AccountEnabled:$false

Mito check, based on CIS Microsoft 365 Foundations Benchmark. Author: oed-metzb; contributors: Mynster9361. Open-source licences.

Open-source licences. CIS Benchmark material © Center for Internet Security, Inc.; CISA SCuBA baselines are public domain (CC0).