Managing Third-Party Risk for CMMC Compliance

Your security is only as strong as your weakest vendor. If a third party with access to your systems or data has poor security, they can undermine your entire CMMC compliance program. Managing third-party risk is not optional—it is essential for protecting Controlled Unclassified Information.

Third-party risk means the potential for vendors, service providers, contractors, and partners to create security vulnerabilities or compliance gaps for your organization.

CUI stands for Controlled Unclassified Information—sensitive government data requiring protection but not classified as secret.

This guide explains how to identify, assess, and manage third-party risks in your CMMC compliance program.

Why Third-Party Risk Matters for CMMC

CMMC requirements do not stop at your organization’s boundaries. Several factors make third-party risk critical:

Shared Responsibility

When vendors access your systems or handle your data, you share security responsibility. Their failures become your failures.

Supply Chain Attacks

Attackers increasingly target vendors to reach their ultimate targets. A compromised vendor can provide attackers access to your environment.

Compliance Inheritance

Some CMMC controls can be inherited from service providers, but only if those providers actually implement them correctly. Relying on non-compliant providers creates gaps.

Assessment Scope

CMMC assessors will examine how you manage third-party access and whether external providers meet appropriate security standards.

Identifying Your Third Parties

Start by inventorying all external parties that could affect your CUI security:

IT Service Providers

• Managed Service Providers (MSPs)
• Cloud service providers
• Software vendors with system access
• IT support contractors

Business Service Providers

• Accounting and payroll services
• Legal services with CUI access
• Consultants working on CUI projects
• Staffing agencies providing personnel

Infrastructure Providers

• Data center and colocation providers
• Internet service providers
• Telecommunications providers
• Physical security services

Contractors and Temporary Workers

• Individual contractors with system access
• Temporary employees
• Interns with CUI exposure

Categorizing Third-Party Risk

Not all vendors pose equal risk. Categorize based on:

Data Access

Category	Risk Level	Examples
Handles CUI directly	Critical	MSP managing CUI systems, cloud storage for CUI
Accesses CUI systems	High	IT support with admin access, software with system integration
Accesses non-CUI systems	Medium	General IT support, business applications
No system or data access	Low	Office supplies, facilities maintenance

Access Type

• Administrative access – Highest risk, can modify security controls
• User-level access – Moderate risk, can access data within permissions
• Physical access only – Lower risk but still relevant for physical security
• No direct access – Lowest risk, but may still have indirect impact

Criticality

• Business critical – Operations depend on this vendor
• Important – Significant impact if vendor fails
• Standard – Replaceable with moderate effort
• Incidental – Minimal impact if relationship ends

Assessing Third-Party Security

For vendors with CUI access or system access, assess their security posture:

Security Questionnaires

Send questionnaires covering:

• Security policies and procedures
• Access control practices
• Encryption capabilities
• Incident response procedures
• Employee background checks
• Compliance certifications

Compliance Certifications

Look for relevant certifications:

• CMMC certification (ideal for defense contractors)
• SOC 2 Type II (demonstrates security controls)
• ISO 27001 (information security management)
• FedRAMP authorization (for cloud services)

SOC 2 stands for Service Organization Control 2—an audit standard for service provider security controls.

FedRAMP stands for Federal Risk and Authorization Management Program—the government authorization standard for cloud services.

Right to Audit

For critical vendors, reserve contractual rights to:

• Review their security documentation
• Conduct security assessments
• Receive notification of security incidents
• Verify compliance with contractual requirements

Continuous Monitoring

Ongoing awareness of vendor security:

• Security rating services (BitSight, SecurityScorecard)
• News monitoring for breaches
• Regular reassessment cycles
• Relationship management conversations

CMMC-Specific Vendor Requirements

Certain CMMC requirements directly address third-party relationships:

External Service Providers (AC.L2-3.1.17)

When using external systems or services, ensure:

• Providers implement required security controls
• Connections are authorized and controlled
• Provider security is documented in your SSP

SSP stands for System Security Plan—the document describing how you implement security requirements.

Controlled Access Points (SC.L2-3.13.6)

Deny network access by default and allow only authorized connections, including connections to external providers.

CUI Protection Responsibilities (Various)

When CUI is shared with or accessible by third parties:

• Ensure they understand CUI handling requirements
• Verify they have appropriate protections
• Document their responsibilities

Contractual Requirements for Vendors

Include appropriate security terms in vendor contracts:

Security Requirements

• Specific security controls they must implement
• Compliance with NIST SP 800-171 or equivalent
• CMMC certification requirements (if applicable)

Data Handling

• How they will protect your data
• Restrictions on data use and sharing
• Data return or destruction upon contract end

Incident Notification

• Requirement to notify you of security incidents
• Timeframe for notification (24-48 hours recommended)
• Information to include in notifications
• Cooperation with incident response

Audit Rights

• Right to review security documentation
• Right to conduct assessments
• Right to receive compliance evidence

Subcontracting Restrictions

• Approval required before subcontracting
• Flow-down of security requirements to their subcontractors
• Notification of subcontractor changes

Managing Ongoing Vendor Relationships

Third-party risk management is ongoing, not one-time:

Regular Reassessment

• Annual security questionnaire updates
• Review of certification renewals
• Assessment after significant changes

Relationship Monitoring

• Track vendor performance
• Monitor for security incidents
• Address concerns promptly

Change Management

• Reassess when vendor services change
• Update contracts when requirements change
• Evaluate when vendors are acquired or merge

Exit Planning

• Plan for transitioning away from vendors
• Ensure data return and destruction provisions
• Document transition procedures for critical vendors

When Vendors Will Not Cooperate

Some vendors resist security assessments:

For Large Vendors:

Large cloud providers and software companies may not complete custom questionnaires. Accept alternatives:

• Published compliance documentation
• SOC 2 reports
• FedRAMP authorizations
• Trust center security information

For Reluctant Vendors:

If vendors will not provide security information:

• Assess whether you need this vendor
• Consider alternatives with better security transparency
• Limit their access to sensitive systems
• Accept the risk with management approval and documentation

For Non-Compliant Vendors:

If assessment reveals inadequate security:

• Require remediation before continuing
• Limit access until issues are resolved
• Find alternative providers
• Document the decision if you accept the risk

Documenting Third-Party Risk Management

CMMC assessors will verify your third-party risk management:

Required Documentation:

• Inventory of third parties with CUI or system access
• Risk assessments for significant vendors
• Security requirements in contracts
• Evidence of vendor security verification
• Incident notification procedures

Evidence to Maintain:

• Completed security questionnaires
• Vendor certifications and attestations
• Contract excerpts showing security terms
• Vendor assessment records
• Ongoing monitoring records

Key Takeaways

Third-party risk management is essential for CMMC compliance. Vendors with access to your systems or CUI can create security vulnerabilities and compliance gaps.

Inventory all third parties, categorize by risk level, and assess security for high-risk vendors. Include appropriate security, data handling, and audit terms in contracts. Monitor vendor relationships continuously.

Document your third-party risk management program to demonstrate compliance during assessment.

Related Articles:

• CMMC Requirements for Managed Service Providers
• External Service Provider Requirements for CMMC
• Microsoft 365 GCC vs GCC High for CMMC
• CMMC Policies and Procedures Requirements
• NIST SP 800-171 Rev 2
• NIST SP 800-161 Rev 1 – Supply Chain Risk Management
• 32 CFR Part 170 – CMMC Program Rule

Official Sources: This article is based on NIST SP 800-171 Revision 2, NIST SP 800-161 Rev 1 (Cybersecurity Supply Chain Risk Management), and 32 CFR Part 170.

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