CISA.MS.EXO.12.2: Safe lists SHOULD NOT be enabled.

ID	CISA.MS.EXO.12.2
Severity	Medium
Suite	CISA SCuBA baselines
Product	Exchange Online
Related products	Defender
Feature	Anti-spam
Security area	Email and collaboration protection
Resource type	Tenant
User impact of fixing	Low
Effort to fix	Low
Benchmark	CISA SCuBA Secure Configuration Baselines for Microsoft 365 ScubaGear main, 2026-10-11, MS.EXO.12.2 (SHOULD)
Framework controls	cisa-scuba:MS.EXO.12.2 nist-800-53-r5:AC-4 Information Flow Enforcement
MITRE ATT&CK	T1566, T1684.002
Reads from	Exchange Online

What this checks and how to fix it

Safe lists SHOULD NOT be enabled.

Rationale: Messages sent from allowed safe list addresses bypass important security mechanisms, including spam filtering and sender authentication checks. Avoiding use of safe lists prevents potential threats from circumventing security mechanisms. While blocking all malicious senders is not feasible, blocking specific known, malicious IP addresses may reduce the threat from specific senders.

Remediation action:

To modify the connection filters, follow the instructions found in Use the Microsoft 365 Defender portal to modify the default connection filter policy.

1. Sign in to Microsoft 365 Defender portal.
2. From the left-hand menu, find Email & collaboration and select Policies and Rules.
3. Select Threat Policies from the list of policy names.
4. Under Policies, select Anti-spam.
5. Select Connection filter policy (Default).
6. Click Edit connection filter policy.
7. Ensure Turn on safe list is not selected.

Related links

• Defender admin center - Anti-spam policies
• CISA 12 IP Allow Lists - MS.EXO.12.2v1
• CISA ScubaGear Rego Reference

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Mito check, based on CISA ScubaGear. Author: soulemike; contributors: merill. Open-source licences.