Managing Shared Responsibility in Cloud Environments for CMMC

More manufacturers and defense contractors are moving systems and data to the cloud every year. 

The operational benefits are real: scalability, reduced infrastructure costs, and easier remote access. But when CUI is involved, cloud adoption introduces a compliance question that too many organizations answer incorrectly, or don’t answer at all.

The question is simple: which CMMC controls belong to you, and which belong to your cloud provider?

Getting that wrong doesn’t just create security gaps. It creates audit findings. And under CMMC, an undocumented or misunderstood cloud compliance boundary can derail an assessment that might otherwise have gone smoothly.

This post explains how cloud compliance and CMMC shared responsibility work in practice, where organizations most often get tripped up, and what your team needs to do to stay on solid ground.

What the Shared Responsibility Model Actually Means

Every major cloud provider operates on a shared responsibility model. The provider secures certain layers of the infrastructure — physical data centers, hypervisors, network fabric, and the underlying platform — while the customer is responsible for everything built on top of that: data, access controls, configurations, monitoring, and identity management.

In a standard business context, this division is straightforward enough. But when CUI enters the picture, the stakes change. 

Under CMMC Level 2, organizations must demonstrate that all 110 NIST 800-171 practices are implemented across every system that processes, stores, or transmits CUI. 

If CUI lives in the cloud, the controls that protect it need to be accounted for — and it needs to be clear who owns each one.

The cloud provider may handle physical security, infrastructure patching, and platform-level encryption. But access control policies, data classification, user management, logging configurations, and incident response procedures almost always remain your responsibility.

If those lines aren’t documented, an assessor will flag it.

Where Organizations Get This Wrong

The most common mistake is assuming the cloud provider “handles security.” They do handle a portion of it. But the portions they don’t handle are exactly the ones assessors focus on during a CMMC evaluation.

Here’s where we see the gaps most often:

  • No documented responsibility matrix. Organizations use cloud services for CUI without ever creating a written record of which controls the provider covers and which they own. Without this document, there’s no way to demonstrate during an assessment that the full control set is accounted for.
  • Default configurations treated as compliant configurations. Cloud platforms ship with default settings that prioritize usability over security. Default access permissions, default logging levels, and default retention periods rarely meet CMMC requirements. If your team hasn’t reviewed and hardened these settings, the environment may be operational but not compliant.
  • Access management handled loosely. Cloud environments make it easy to grant access — and just as easy to forget about it. We regularly see CUI stored in cloud platforms where former employees, contractors, or unnecessary service accounts still have active permissions. Under NIST 800-171, access to CUI must be limited to authorized users and reviewed periodically.
  • Logging and monitoring gaps. CMMC requires audit logs that capture specific event types and are retained for a defined period. Many cloud platforms offer logging capabilities, but they need to be turned on, configured correctly, and integrated with your monitoring workflow. If your cloud logs aren’t being reviewed or aren’t capturing the right events, that’s a gap an assessor will identify.
  • Incident response doesn’t account for the cloud. Your incident response plan may cover on-premises systems thoroughly but say nothing about how a security event in your cloud environment would be detected, escalated, or contained. If CUI is in the cloud, your IR plan needs to address it specifically.

What Your Team Needs to Do

Managing cloud compliance for CMMC shared responsibility comes down to documenting clearly, configuring deliberately, and reviewing regularly. 

Here’s a practical checklist your IT team or MSP can follow.

Map CUI in the cloud. Identify every cloud service that stores, processes, or transmits CUI. This includes productivity platforms (Microsoft 365, Google Workspace), file storage services, hosted databases, and SaaS tools. If CUI touches it, it belongs in your data flow diagram and your SSP.

Build a shared responsibility matrix. For each cloud service handling CUI, create a document that maps every applicable NIST 800-171 control to the responsible party — either your organization or the cloud provider. Use your provider’s published shared responsibility documentation as a starting point, then validate each line item against your actual configuration.

Harden configurations beyond defaults. Review authentication settings, access permissions, encryption options, session timeouts, and data retention policies. Compare them against CMMC requirements and your organization’s security policies. Document every configuration decision and the rationale behind it.

Enforce access control discipline. Implement role-based access for cloud platforms handling CUI. Review permissions quarterly. Remove access for terminated employees and inactive accounts promptly. Use multi-factor authentication for every user with access to CUI environments.

Configure logging to meet audit requirements. Enable logging for authentication events, access attempts, configuration changes, and data transfers. Confirm that log retention meets CMMC-required timeframes. Integrate cloud logs with your SIEM or monitoring platform so they’re reviewed alongside on-premises activity, not in isolation. If your organization uses EDR/XDR monitoring, ensure cloud endpoints are included in that coverage.

Update your incident response plan. Add cloud-specific scenarios to your IR plan. Define how your team would detect a compromise in a cloud environment, who would be notified, what containment steps are available through the platform, and how you would preserve evidence. If your cloud provider has its own incident notification process, document how that integrates with yours.

Review vendor agreements. Examine your cloud provider’s terms of service, data processing agreements, and security commitments. Confirm that their obligations align with what you’ve documented in your shared responsibility matrix. If there are gaps between what the provider commits to and what CMMC requires, those gaps are yours to fill.

Keep It Current

Cloud environments change frequently. New services get added, configurations drift, personnel rotate, and providers update their own policies. 

A shared responsibility matrix that was accurate six months ago may not reflect your current state.

Build a recurring review into your compliance program — quarterly at minimum — to validate that your cloud documentation, configurations, and access controls still align with what your SSP describes. The organizations that treat cloud compliance as a living process are the ones that stay assessment-ready without scrambling.

Where DataSure24 Fits

Our team works with manufacturers, contractors, and MSPs to evaluate cloud environments for CMMC readiness, build shared responsibility documentation, and identify configuration gaps before they become assessment findings. 

Through our CMMC Services and EDR/XDR monitoring capabilities, we help organizations bring their cloud compliance into alignment with the rest of their security program.

Have questions about your CMMC program? Schedule a time to talk with our team at datasure24.com.