Microsoft 365
TMA-M365-1.3.3
Ensure 'External sharing' of calendars is not available
Description
External calendar sharing allows an administrator to enable the ability for users to share calendars with anyone outside of the organization. Outside users will be sent a URL that can be used to view the calendar. Attackers often spend time learning about organizations before launching an attack. Publicly available calendars can help attackers understand organizational relationships and determine when specific users may be more vulnerable to an attack, such as when they are traveling.
How it is checked
Audit method: Manual review
To audit using the UI: 1. Navigate to Microsoft 365 admin center https://admin.microsoft.com. 2. Expand Settings > Org settings. 3. In the Services section click Calendar. 4. Verify that Let your users share their calendars with people outside of your organization who have Office 365 or Exchange is unchecked. To audit using PowerShell: 1. Connect to Exchange Online using Connect-ExchangeOnline. 2. Run the following Exchange Online PowerShell command: Get-SharingPolicy -Identity "Default Sharing Policy" | ft Name,Enabled 3. Verify that Enabled is set to False
How it is fixed
Fix method: Guidance or infrastructure patch
To remediate using the UI: 1. Navigate to Microsoft 365 admin center https://admin.microsoft.com. 2. Expand Settings select Org settings. 3. In the Services section click Calendar. 4. Uncheck Let your users share their calendars with people outside of your organization who have Office 365 or Exchange. 5. Click Save. To remediate using PowerShell: 1. Connect to Exchange Online using Connect-ExchangeOnline. 2. Run the following Exchange Online PowerShell command: Set-SharingPolicy -Identity "Default Sharing Policy" -Enabled $False
Properties
- Operating systems
- Any
- Tags
- m365saas
- Reference
- CIS Microsoft 365 Foundations Benchmark v7.0.0 - 1.3.3 Ensure 'External sharing' of calendars is not available