Microsoft 365
TMA-M365-2.1.13
Ensure the connection filter safe list is off
Description
In Microsoft 365 organizations with Exchange Online mailboxes or standalone Exchange Online Protection (EOP) organizations without Exchange Online mailboxes, connection filtering and the default connection filter policy identify good or bad source email servers by IP addresses. The key components of the default connection filter policy are IP Allow List, IP Block List and Safe list. The safe list is a pre-configured allow list that is dynamically updated by Microsoft. The recommended safe list state is: Off or False Without additional verification like mail flow rules, email from sources in the IP Allow List skips spam filtering and sender authentication (SPF, DKIM, DMARC) checks. This method creates a high risk of attackers successfully delivering email to the Inbox that would otherwise be filtered. Messages that are determined to be malware or high confidence phishing are filtered....
How it is checked
Audit method: Manual review
To audit using the UI: 1. Navigate to Microsoft Defender https://security.microsoft.com. 2. Expand Email & collaboration > Policies & rules > Threat policies. 3. Under Policies select Anti-spam. 4. Click on the Connection filter policy (Default). 5. Verify that Safe list is Off. To audit using PowerShell: 1. Connect to Exchange Online using Connect-ExchangeOnline. 2. Run the following PowerShell command: Get-HostedConnectionFilterPolicy -Identity Default | fl EnableSafeList 3. Verify that EnableSafeList is False
How it is fixed
Fix method: Guidance or infrastructure patch
To remediate using the UI: 1. Navigate to Microsoft Defender https://security.microsoft.com. 2. Expand Email & collaboration > Policies & rules> Threat policies. 3. Under Policies select Anti-spam. 4. Click on the Connection filter policy (Default). 5. Click Edit connection filter policy. 6. Uncheck Turn on safe list. 7. Click Save. To remediate using PowerShell: 1. Connect to Exchange Online using Connect-ExchangeOnline. 2. Run the following PowerShell command: Set-HostedConnectionFilterPolicy -Identity Default -EnableSafeList $false
Properties
- Operating systems
- Any
- Tags
- m365saas
- Reference
- CIS Microsoft 365 Foundations Benchmark v7.0.0 - 2.1.13 Ensure the connection filter safe list is off