CIS.M365.2.1.4 - (L2) Ensure Safe Attachments policy is enabled (Only Checks Default Policy)

Contributed by Ben Miles with 2 co-contributorsAll contributors →

Overview

2.1.4 (L2) Ensure Safe Attachments policy is enabled

The Safe Attachments policy helps protect users from malware in email attachments by scanning attachments for viruses, malware, and other malicious content. When an email attachment is received by a user, Safe Attachments will scan the attachment in a secure environment and provide a verdict on whether the attachment is safe or not.

Rationale

Enabling Safe Attachments policy helps protect against malware threats in email attachments by analyzing suspicious attachments in a secure, cloud-based environment before they are delivered to the user's inbox. This provides an additional layer of security and can prevent new or unseen types of malware from infiltrating the organization's network.

Impact

Delivery of email with attachments may be delayed while scanning is occurring

Remediation action

To enable the Safe Attachments policy:

1. Navigate to Microsoft 365 Defender.
2. Click to expand E-mail & Collaboration select Policies & rules.
3. On the Policies & rules page select Threat policies.
4. Under Policies select Safe Attachments.
5. Click + Create.
6. Create a Policy Name and Description, and then click Next.
7. Select all valid domains and click Next.
8. Select Block.
9. Quarantine policy is AdminOnlyAccessPolicy.
10. Leave Enable redirect unchecked.
11. Click Next and finally Submit.

PowerShell

1. Connect to Exchange Online using Connect-ExchangeOnline.
2. To change an existing policy modify the example below and run the following PowerShell command:

Set-SafeAttachmentPolicy -Identity 'Example policy' -Action 'Block' -QuarantineTag 'AdminOnlyAccessPolicy' -Enable $true

3. Or, edit and run the below example to create a new safe attachments policy.

New-SafeAttachmentPolicy -Name "CIS 2.1.4" -Enable $true -Action 'Block' -QuarantineTag 'AdminOnlyAccessPolicy'

New-SafeAttachmentRule -Name "CIS 2.1.4 Rule" -SafeAttachmentPolicy "CIS 2.1.4" -RecipientDomainIs 'exampledomain[.]com'

Note: Policy targets such as users and domains should include domains, or groups that provide coverage for a majority of users in the organization. Different inclusion and exclusion use cases are not covered in the benchmark.

Related links

• Microsoft 365 Defender
• Safe Attachments in Microsoft Defender for Office 365
• Set up Safe Attachments policies in Microsoft Defender for Office 365
• CIS Microsoft 365 Foundations Benchmark v7.0.0 - Page 92

Test Metadata

Field	Value
Test ID	CIS.M365.2.1.4
Severity	High
Suite	CIS
Product	Defender
Related products	Exchange Online
Feature	Safe Attachments
Area	Email and collaboration protection
Resource type	Tenant
User impact	Low
Implementation cost	Low
MITRE ATT&CK	T1566.001 Spearphishing Attachment, T1204.002 Malicious File
Supports benchmark	CIS Microsoft 365 Foundations Benchmark (version 7.0.0), requirement 2.1.4
Benchmark level	L2
Benchmark profiles	E5 Level 2
Supports controls	cis-m365:2.1.4, nist-800-53-r5:SI-3
PowerShell test	Test-MtCisSafeAttachment
Services	ExchangeOnline, Graph, SecurityCompliance
Compatible licenses	ATP_ENTERPRISE

Source

• Test: tests/cis/Test.CIS.M365.2.1.4.ps1
• Documentation: tests/cis/Test.CIS.M365.2.1.4.md