CMMC and Microsoft 365 GCC High: What Changes for CUI

Why GCC High Shows Up in CMMC Programmes

• Supports DoD / federal CUI handling expectations better than commercial tenants
• Aligns identity, storage, and admin planes to US Government cloud boundaries
• Enables clearer scoping when CUI mail and files leave commercial Microsoft 365

Customer Controls That Still Fail Assessments

• Over-broad guest access and unmanaged devices reaching CUI libraries
• Missing MFA / privileged access workstations for Global Admin roles
• Incomplete audit log retention and SIEM forwarding for AU family evidence
• Shadow IT (personal OneDrive, commercial Teams) still holding CUI
• ESP/MSP admin access without contracts and monitoring

Practical Migration Checklist

1. Classify data: FCI vs CUI vs public; stop CUI creation in commercial tenants.
2. Redraw the assessment boundary.
3. Rebuild identity: Conditional Access, PIM/PAM patterns, device compliance.
4. Forward unified audit logs to a SIEM with review procedures.
5. Update the SSP and SPRS narrative to match the new enclave.

How CyberSilo Helps

• CSA maps M365 configuration evidence to 800-171 requirement IDs
• ThreatHawk ingests Microsoft audit / security signals for AU/SI sampling
• We do not sell Microsoft licenses; we help evidence the programme around them

Frequently Asked Questions

Is GCC High mandatory for every CMMC Level 1 company?

Level 1 addresses FCI via 15 FAR basic safeguarding requirements. Many L1 environments never need GCC High; CUI-centric Level 2 programmes commonly do. Follow your data types and contracts.

Does GCC High satisfy all 110 Level 2 requirements?

No. It supports inherited cloud controls. Customer identity, endpoints, IR, media, personnel, and many operational processes remain yours.

Should logs stay only in Microsoft Purview?

Retention and review must meet your SSP. Many OSCs forward to a SIEM for correlation and assessor sampling — see our AU guide.

Related CMMC Resources

CMMC hub · FedRAMP equivalency · CMMC vs FedRAMP · SSP · Checklist