CIS.M365.2.1.3: Ensure notifications for internal users sending malware is Enabled (Only Checks Default Policy)

CIS Benchmark notice

This check implements a recommendation of the CIS Microsoft 365 Foundations Benchmark. The benchmark text is © Center for Internet Security, Inc. and is not reproduced here beyond the short summary below. Get the full benchmark free of charge from cisecurity.org.

ID	CIS.M365.2.1.3
Severity	Medium
Suite	CIS Microsoft 365 Foundations Benchmark
Product	Defender
Related products	Exchange Online
Feature	Anti-malware
Security area	Email and collaboration protection
Resource type	Tenant
User impact of fixing	Low
Effort to fix	Low
Benchmark	CIS Microsoft 365 Foundations Benchmark 7.0.0, 2.1.3 (L1, E3 Level 1)
Framework controls	cis-m365:2.1.3 nist-800-53-r5:SI-4(5) System Monitoring | System-generated Alerts
MITRE ATT&CK	T1534
Reads from	Exchange Online, Security & Compliance PowerShell

What this checks and how to fix it

2.1.3 (L1) Ensure notifications for internal users sending malware is Enabled

Exchange Online Protection (EOP) is Microsoft’s cloud-based filtering service that protects organizations against spam, malware, and other email threats. EOP is included in all Microsoft 365 organizations with Exchange Online mailboxes.

EOP uses flexible anti-malware policies for malware protection settings. These policies can be set to notify Admins of malicious activity.

Rationale

This setting alerts administrators that an internal user sent a message that contained malware. This may indicate an account or machine compromise that would need to be investigated.

Impact

Notification of account with potential issues should not have an impact on the user

Remediation action

To enable notifications for internal users sending malware:

1. Navigate to Microsoft 365 Defender https://security.microsoft.com.
2. Click to expand E-mail & Collaboration select Policies & rules.
3. On the Policies & rules page select Threat policies.
4. Under Policies select Anti-malware.
5. Click on the Default (Default) policy.
6. Click on Edit protection settings and change the settings for Notify an admin about undelivered messages from internal senders to On and enter the email address of the administrator who should be notified under Administrator email address.
7. Click Save.

PowerShell

1. Connect to Exchange Online using Connect-ExchangeOnline.
2. Run the following command:

Set-MalwareFilterPolicy -Identity '{Identity Name}' -EnableInternalSenderAdminNotifications $True -InternalSenderAdminAddress {admin@domain1.com}

Note: Audit and Remediation guidance may focus on the Default policy however, if a Custom Policy exists in the organization’s tenant, then ensure the setting is set as outlined in the highest priority policy listed.

Related links

• Microsoft 365 Defender
• Anti-malware protection for cloud mailboxes
• Configure anti-malware policies for cloud mailboxes
• CIS Microsoft 365 Foundations Benchmark v7.0.0 - Page 88

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Mito check, based on CIS Microsoft 365 Foundations Benchmark. Author: NZLostboy; contributors: thomas-s-schmidt, Mynster9361. Open-source licences.