Enforcing Software Restrictions Through System Configuration
CM.L2-3.4.9[b] is the enforcement-focused assessment objective for controlling what software can run in your environment. After you define how unauthorized software is prevented (the related planning and definition work typically documented under your software control approach), this objective requires you to show that execution restrictions are implemented in technical configuration and applied in practice. Assessors validate that systems are configured to block or restrict unauthorized executables, that enforcement applies to in-scope endpoints and systems, and that the configuration is maintained over time rather than being a one-time setup.
The intent is straightforward: your environment should not permit unapproved or unknown software to execute by default. Instead, software execution should be governed by defined rules such as application allowlisting, software restriction policies, or endpoint execution control features that actively prevent untrusted programs from running.
What Assessors Validate for CM.L2-3.4.9[b]
Assessors typically evaluate whether execution controls are active, consistently applied, and aligned to your documented policy. This objective is commonly validated by reviewing real system settings (not only policy documents) and by examining artifacts that demonstrate enforcement outcomes. In practical terms, assessors expect to see that:
- Execution controls are technically configured to block or restrict unauthorized software.
- The chosen control mechanism is appropriate for the platforms in scope (for example, Windows endpoints, managed mobile devices, or Linux systems).
- Policies are deployed broadly to relevant systems and users rather than limited to a subset of endpoints.
- Enforcement is enabled (not limited to monitoring or audit-only mode where execution still occurs).
- Configurations and allowlists are maintained and updated as the approved software set changes.
Organizations often connect these implementation details to their broader NIST 800-171 compliance and assessment preparation activities by ensuring that software control policies, exception handling, and operational reviews are documented and traceable to technical enforcement.
Why Execution Restrictions Matter for Protecting CUI
Execution restrictions reduce exposure to malware, ransomware, and unauthorized tools that can introduce backdoors, capture credentials, or exfiltrate Controlled Unclassified Information (CUI). When untrusted software is allowed to run unchecked, endpoints become a frequent initial access point for compromise, and insider misuse becomes harder to detect and contain. Strong software execution controls also help stabilize the configuration of systems by preventing ad hoc installations that can create untracked dependencies, unapproved remote access utilities, or noncompliant data handling paths.
From an audit perspective, enforcement provides objective evidence that the organization maintains control of the system environment. This is particularly important where users have local execution capability, where removable media is used, or where endpoints connect to external networks. Demonstrable enforcement supports consistent outcomes across the CUI boundary and helps reduce variance between “policy intent” and “operational reality.”
Implementation Approaches for Enforced Software Restrictions
Windows execution controls
For Windows systems, implementation commonly relies on platform-native controls such as AppLocker or Windows Defender Application Control (WDAC), configured to enforce allowlisting by path, publisher signature, hash, or packaged app identity. A common assessor focus is whether the policy is deployed via centralized management (for example, Group Policy) and whether the mode is enforcement rather than audit-only.
Endpoint control platforms
Many organizations implement execution restrictions using endpoint security platforms that support application control or execution blocking. In these cases, assessors typically look for the specific rule sets that restrict execution, the scope of deployment across in-scope endpoints, and evidence that blocked execution events are recorded and reviewed.
MDM-enforced controls for managed devices
For managed devices governed by mobile device management (MDM), enforcement typically includes application allowlisting, installation restrictions, or device compliance policies that prevent unapproved executables or apps from being installed or launched. Implementation should specify how policies are pushed, how exceptions are handled, and how drift is detected when devices fall out of compliance.
Linux integrity and execution confinement
For Linux systems, organizations may use mandatory access control frameworks such as SELinux or AppArmor, combined with file permissions and controlled package repositories, to limit executable behavior and reduce the risk of unauthorized binaries. Assessors typically validate that controls are enabled and applied consistently, not merely installed.
Operational Requirements to Keep Enforcement Effective
Execution controls require ongoing maintenance. Allowlists must reflect the organization’s approved software set, and changes should follow documented approval and testing. Periodic validation helps ensure controls do not drift into permissive configurations. Organizations preparing for CMMC compliance often formalize an operating cadence that includes reviewing blocked execution events, evaluating exception requests, and retesting enforcement after major system updates or policy changes.
Testing should confirm that unauthorized software is blocked as expected. The goal is not to test every possible executable, but to demonstrate that the enforcement mechanism functions reliably and that evidence is captured when blocks occur.
Evidence Assessors Commonly Request
- Screenshots or exports of application control configurations showing enforcement settings.
- Policy deployment records demonstrating coverage across in-scope endpoints.
- System, endpoint, or SIEM logs showing attempted execution of blocked software.
- Documentation linking system settings to the organization’s software control policy and approved software definitions.
- Records of periodic testing or validation that unauthorized software is prevented from running.
Common Gaps That Create Findings
- Execution controls are deployed but not set to enforcement mode.
- Only audit logging is enabled, allowing unauthorized software to execute.
- Allowlist definitions are inconsistent, outdated, or not tied to an approval process.
- Policies are applied to some endpoints but not all systems within scope.
- Evidence exists in configuration, but logs and review artifacts do not demonstrate ongoing operational oversight.
Implementation and Evidence Mapping Table
| Implementation area | Required configuration outcome | Assessor validation method | Evidence to retain |
|---|---|---|---|
| Execution policy mode | Enforcement enabled (not audit-only) | Review policy settings in management console | Configuration export or screenshots showing enforcement |
| Policy coverage | Applied to all relevant in-scope endpoints/systems | Validate deployment scope and targeting | Deployment reports; endpoint compliance status |
| Allowlist definition | Only approved software or signatures permitted | Examine rules for paths, publishers, hashes, or app identities | Allowlist rule export; approved software list reference |
| Blocked execution visibility | Blocked events are recorded and retained | Review endpoint logs or SIEM events for blocks | Log samples of denied execution attempts |
| Ongoing maintenance | Changes reviewed, tested, and documented | Verify change records and periodic validation | Change tickets; test records; review notes |
FAQ
What does CM.L2-3.4.9[b] require?
It requires technical enforcement that blocks or restricts unauthorized software execution using configured controls such as allowlisting or restriction policies.
What evidence supports this objective during assessment?
Assessors typically review execution control settings, deployment scope, logs showing blocked software attempts, and documentation linking configuration to the software control policy.
What is a common gap for this objective?
A frequent gap is having application control deployed in audit-only mode, where events are logged but unauthorized software can still run.