RA.L2-3.11.2 in the CMMC 2.0 / NIST SP 800-171 Rev.2 context requires regular vulnerability scanning and analysis of organizational systems to identify and address weaknesses that could expose controlled unclassified information (CUI); this post explains how to implement that requirement in a small-business environment using Tenable Nessus, with concrete scan templates, credentialed scanning advice, remediation workflows, and audit evidence practices.
Understanding RA.L2-3.11.2 and Compliance Framework Objectives
At its core, RA.L2-3.11.2 asks organizations to establish a repeatable vulnerability scanning program that identifies vulnerabilities, supports prioritization and remediation, and produces artifacts for compliance validation; for small businesses working under the Compliance Framework this means proving a documented scanning cadence, authenticated checks where possible, tracking remediation in a POA&M (Plan of Actions & Milestones), and retaining scan evidence (reports, configs, remediation tickets) for audits.
Implementation Overview Using Nessus
Start by deploying a central Nessus (or Tenable Vulnerability Management) scanner appliance in your network and, where needed, install Nessus Agents for remote or intermittently connected endpoints (laptops, remote contractors). Define asset inventories and tags (e.g., CUI_Servers, DMZ, Workstations) in Nessus so scans are scoped and repeatable. For cloud-hosted workloads, deploy Nessus in the same cloud region/VPC or use API connectors and ensure IAM roles allow host enumeration and port/protocol checks. Keep a single authoritative asset list that maps to your Configuration Management Database (CMDB) or inventory spreadsheet used for compliance evidence.
Scan Templates & Naming Conventions (practical)
Create a small set of reproducible Nessus scan templates aligned with the Compliance Framework. Example templates: "RA-L2-3.11.2 - Credentialed Internal Weekly", "RA-L2-3.11.2 - External Perimeter Daily", "RA-L2-3.11.2 - Post-Patch Validation - 48h", and "RA-L2-3.11.2 - Agent Inventory & Quick Scan". For each template define: port range (TCP 1-65535; UDP scan limited to top 100/200 ports for performance), plugin set (Full and fast + Local Security Checks for authenticated scans), and performance tuning (Max simultaneous checks per host 5–10 depending on environment). Name templates and scheduled jobs to include the requirement code (RA.L2-3.11.2) so auditors can quickly find relevant artifacts.
Authenticated (Credentialed) Scanning - Technical Details
Authenticated scans dramatically reduce false positives and are required by many assessors for meaningful coverage. For Windows: use a domain or local account with local admin membership (or equivalent rights) and enable SMB/WMI-based checks; supply either username/password or domain\\user and test connectivity before scheduling. For Linux: use an SSH account with sudo privileges (or root where policy permits) and prefer key-based authentication for security. In Nessus Advanced Scan settings enable "Perform comprehensive tests" and "Use configuration audit" where applicable; also add registry/file checks for CUI-specific configurations (e.g., encryption settings). Use Nessus Agents for mobile or remote hosts where opening management ports is impractical—agents perform local checks and forward results to the manager, preserving continuous coverage even for off-network devices.
Scheduling, Cadence, and Remediation Workflow
Define a scanning cadence that maps to risk and CMMC expectations: external perimeter scans daily, internal authenticated scans weekly (or at least monthly), and targeted post-patch scans within 24–72 hours after patch deployments. Configure Nessus to export machine-readable reports (CSV and .nessus/.xml) and human-readable PDFs; integrate with your ticketing system (Jira, ServiceNow) via API or use Tenable connectors to auto-create remediation tickets for findings above a defined severity (e.g., CVSS >= 7 Critical, CVSS 4–6.9 High). Maintain a remediation SLA matrix in your POA&M (for CUI systems: Critical within 15 days, High 30 days, Medium 60 days — adjust to your contractual needs and risk appetite) and attach scan evidence showing remediation (re-scan results) when closing tickets.
Small-Business Examples, Scenarios, and Best Practices
Example 1 — Small defense subcontractor with 30 endpoints: deploy a single Nessus Professional on-premises, use agents on laptops, schedule weekly authenticated scans for the internal LAN, and weekly external scans via a cloud-hosted Nessus scanner or Tenable.io; keep CSV exports and PDFs in a secure evidence repository (versioned). Example 2 — SMB with cloud workloads: run Nessus in an EC2 instance with an IAM role allowing host discovery, tag EC2 instances for scan targeting, and use agent scans for ephemeral containers. Best practices: use maintenance windows to avoid disruption, exclude backups/sensitive IoT from intrusive scans (document exclusions), and tune UDP scans to minimize load (or run during off-hours).
Risk of Non-Implementation and Audit Evidence
Failing to implement RA.L2-3.11.2 exposes CUI to unpatched vulnerabilities, increases the chance of lateral movement from an external compromise, and can result in contract penalties or loss of DoD work. For auditors, absence of scheduled scans, authenticated scan configurations, remediation tickets, and re-test evidence typically results in non-compliance findings. Retain: (1) scan policies and template exports that show settings, (2) scheduled job logs, (3) raw .nessus scan files and exported CSVs, (4) remediation tickets with links to scan IDs, and (5) re-scan reports demonstrating closure; these items collectively form the evidence package for the Compliance Framework assessment.
Compliance Tips and Practical Controls
Maintain a written scanning policy that references RA.L2-3.11.2, include exception approval processes, and hard-code scan naming conventions that reference the control. Prioritize remediation using exploitability and asset criticality (CUI servers first). Regularly review and update credential accounts used by Nessus (rotate service accounts and keys), and restrict scanner access using network access control so the scanner itself is protected. Periodically run a secondary validation with a different tool or third-party assessor to avoid blind spots. Finally, automate as much evidence collection as possible: scheduled exports, auto-ticketing for findings above thresholds, and tagged rescan jobs to prove remediation.
In summary, meeting RA.L2-3.11.2 with Nessus requires a documented asset inventory, a small set of repeatable scan templates (credentialed internal, external perimeter, post-patch), a defined remediation workflow with SLAs and POA&M entries, and retained evidence for audits; for small businesses, a pragmatic combination of Nessus Agents, credentialed scans, scheduled jobs, and automated ticketing provides both strong security posture and the artifacts needed to demonstrate compliance under the Compliance Framework.
