CISA.MS.EXO.6.1 - Contact folders SHALL NOT be shared with all domains.
Overview
Contact folders SHALL NOT be shared with all domains.
Rationale: Contact folders may contain information that should not be shared by default with all domains. Disabling sharing with all domains closes an avenue for data exfiltration while still allowing for specific legitimate use as needed.
Remediation action:
To restrict sharing with all domains:
- Sign in to the Exchange admin center.
- On the left-hand pane under Organization, select Sharing.
- Select Individual Sharing.
- For all existing policies, select the policy, then select Manage domains.
- For all sharing rules under all existing policies, ensure Sharing with everyone and Anonymous do not include ContactsSharing.
Related links
- Exchange admin center - Individual Sharing
- CISA 6 Calendar and Contact Sharing - MS.EXO.6.1v1
- CISA ScubaGear Rego Reference
Test Metadata
| Field | Value |
|---|---|
| Test ID | CISA.MS.EXO.6.1 |
| Severity | Medium |
| Suite | CISA |
| Product | Exchange Online |
| Feature | Calendar and contact sharing |
| Area | External access and sharing |
| Resource type | Policy |
| User impact | Low |
| Implementation cost | Low |
| MITRE ATT&CK | T1048 Exfiltration Over Alternative Protocol, T1567 Exfiltration Over Web Service |
| Supports benchmark | CISA SCuBA Secure Configuration Baselines for Microsoft 365 (version ScubaGear main, 2026-10-11), requirement MS.EXO.6.1 |
| Criticality | SHALL |
| Upstream requirement | MS.EXO.6.1v1 |
| Supports controls | cisa-scuba:MS.EXO.6.1, nist-800-53-r5:AC-3, nist-800-53-r5:SC-7(10)(a) |
| PowerShell test | Test-MtCisaContactSharing |
| Services | ExchangeOnline |
Source
- Test:
tests/cisa/exchange/Test.CISA.MS.EXO.6.1.ps1 - Documentation:
tests/cisa/exchange/Test.CISA.MS.EXO.6.1.md