Common CMMC Mistakes: Treating CMMC Assessment Like a Snapshot in Time

Top 15 Most Common CMMC Compliance Mistakes Series #4

This article is part of our expert-led series: The Top 15 Most Common CMMC Compliance Mistakes (and How to Solve Them). Throughout this series, we're dissecting the frequent errors, misunderstandings, and misconceptions organizations encounter on their path to CMMC certification, drawing insights from seasoned CCPs, CISOs, and CCAs.

Today’s focus:  We discuss why a successful CMMC assessment requires months of proven compliance, not last-minute fixes, and how to meet auditor expectations.

What You’ll Learn

• Why CMMC assessments require 90+ days of evidence, not last-minute checklists
• What auditors are really looking for (and how to provide it)
• How to align your policies, practices, and culture to meet maturity expectations
• What role supply chain and vendor risk management plays in your audit
  
  

Why CMMC Isn’t a One-Day Event

There’s a misconception that if a company quickly documents policies or spins up a logging tool the week before their assessment, they’ll pass. That’s not how it works. CMMC Level 2 is designed to assess not just the presence of controls, but the maturity of those controls. Auditors need to see operational consistency over time.

CMMC is a snapshot of your cybersecurity posture, but that snapshot must show the outcomes of a long history of implementation. As the official CMMC Assessment Guide, Level 2 notes, assessment objectives often require historical documentation, logged activity, and personnel behavior that proves controls have been in effect and functioning as intended for a minimum period, often 90 days or more.

The 90-Day Rule and Historical Evidence

CMMC requirements aren’t theoretical. They come with tangible expectations, especially when it comes to showing that the framework has been operating as part of your organization for at least three months prior to your C3PAO assessment.

Specific practices that require this historical evidence include:

If your system logs were activated just days before your scheduled audit, or if access reviews were “done” in theory but not documented, auditors will not accept that as sufficient.

What Auditors Look for During Assessment

Assessors are trained to look past documentation and validate operational maturity. Some of the most frequently requested artifacts during a Level 2 assessment include:

• Audit logs spanning 90+ days
  
  
• Proof of vulnerability management cycles (scans and patching reports)
  
  
• Documentation of periodic access reviews
  
  
• Results and participation rosters for tabletop exercises
  
  
• Evidence that leadership is reviewing cybersecurity progress
  
  
• Change control records
  
  
• Incident response testing logs
  
  

A strong System Security Plan (SSP) should point directly to these artifacts and include descriptions of how each is maintained and reviewed. If an artifact doesn’t exist or doesn’t have historical depth, you may not meet the requirement.

Culture Change Can’t Be Faked

A critical, often overlooked aspect of readiness is culture. True CMMC compliance means cybersecurity is part of how your company operates, not just something IT handles. A well-developed program should show evidence that:

• Leadership actively promotes cybersecurity goals
  
  
• Employees complete annual training and understand how to handle CUI
  
  
• Policies are followed, updated, and reinforced
  
  
• There is a consistent rhythm to security activities across all departments
  
  

Rushing to “check boxes” days before the audit not only risks failure but shows auditors that your organization hasn't adopted the spirit of the CMMC framework.

Don’t Forget the Supply Chain

Another easily neglected area is Vendor Risk Management. Many companies fail to realize that their responsibility extends to their suppliers. Under DFARS 252.204-7012 and CMMC Level 2, you're required to manage and document how your vendors protect CUI, especially those with downstream access.

This includes:

• Annual vendor security reviews
  
  
• Proof of flow-down clauses in contracts
  
  
• Due diligence logs for new third-party vendors
  
  

These records must exist before your audit and be part of a larger supplier risk strategy, not thrown together at the last minute.

How to Build an Assessment-Ready Compliance Culture

Preparing for your CMMC assessment is less about documentation and more about running a consistent, auditable program that works day in and day out. Here’s how:

• Implement key logging and auditing tools early, and test them regularly
  
  
• Use your SSP to clearly map each control to supporting artifacts
  
  
• Run internal risk assessments at least annually, and document follow-ups
  
  
• Schedule recurring compliance reviews months before the C3PAO engagement
  
  
• Make cybersecurity a leadership issue, not just an IT function

In Summary: Walking the Walk Before you Talk the Talk

Rushing into a CMMC assessment without historical implementation is a fast track to failure. You need to prove your systems, policies, and procedures have been operational for months, not days.

Key Takeaways

• CMMC assessments validate maturity, not just existence of controls
• 90-day implementation evidence is often required for core practices
• Vendor risk management must be documented and recurring
• Leadership and cultural adoption are crucial for long-term compliance

Up Next In Our Top 15 Most Common CMMC Mistakes Series:

In our next article, we'll discuss how failing to read and understand the details of cybersecurity clauses in contracts can lead to major compliance failures. Learn how to avoid missteps with expert cybersecurity contract review.