This post explains how to configure Nessus to satisfy NIST SP 800-171 Rev.2 / CMMC 2.0 Level 2 control RA.L2-3.11.2—focusing on scan policies, credentialed scanning, and remediation workflows—providing practical steps, small-business examples, and compliance best practices relevant to the Compliance Framework.
Understanding RA.L2-3.11.2 and mapping it to Nessus
RA.L2-3.11.2 requires organizations to regularly scan for vulnerabilities and misconfigurations, use credentialed scanning where feasible, and integrate scanning outputs into remediation processes. For Compliance Framework implementers this means: (1) creating and documenting scan policies that align with the sensitivity of Controlled Unclassified Information (CUI), (2) using authenticated (credentialed) checks to detect missing patches and insecure configurations, and (3) establishing repeatable remediation and verification workflows that produce audit evidence. Nessus (Professional, Manager, or Tenable.io backed scanners) is well-suited because it supports credentialed checks, compliance auditing plugins, scheduling, reporting, and APIs for ticketing integration.
Building scan policies and credentialed scans in Nessus
Start by creating separate scan policies for CUI-bearing assets versus general corporate hosts. Practical settings include a full TCP port scan (1-65535) for discovery, enabling UDP probes for services you use, and activating plugin families for "Patch Audit" and "Policy Compliance". For Windows, enable SMB and WinRM/PowerShell-based checks (ports 445, 5985, 5986) and for *nix machines use SSH (port 22). Configure reasonable port and timeout values (e.g., 1-2s probe timeout, 4-5 retries for flaky networks) to limit scan impact. Schedule full authenticated scans monthly for CUI systems, weekly authenticated scans for internet-facing assets, and daily unauthenticated quick scans for high-change zones (developers, test systems).
Credential types and least-privilege recommendations
Use dedicated, least-privilege service accounts for authenticated scanning: Windows domain service accounts with local administrator rights only where necessary, or accounts granted explicit rights (WMI/WinRM) using group policies. For Linux, prefer SSH keys with sudo privileges limited to the checks Nessus needs (or configure sudoers to allow passwordless execution of specific commands). Avoid using domain admin credentials; instead leverage local admin accounts managed by Microsoft LAPS for workstations and servers to reduce credential exposure. Store credentials securely in Nessus/Tenable's credential vault or an external secrets manager (HashiCorp Vault, Azure Key Vault) and rotate regularly—document rotation schedule as part of your Compliance Framework evidence.
Configuring credentialed checks for patching and compliance
Enable plugin families that focus on missing patches, insecure configurations (CIS benchmarks, STIGs where applicable), and configuration checks that map to NIST 800-171 requirements (e.g., password policies, logging configuration). For Windows patch audits, enable SMB-based patch checks and PowerShell/WinRM checks to read installed hotfix lists; for Linux, enable package manager checks (rpm/apt) via SSH. Use Nessus report filters to map findings to severity levels: treat Critical/High CVEs and missing security updates as top priority. Export and keep the plugin output and scan diffs (pre/post remediation scans) as artifacts for auditors to demonstrate remediation verification.
Remediation workflows and integration with ticketing systems
A compliant remediation workflow ties scanning to action: 1) schedule and run scans, 2) triage and prioritize findings by severity and CUI impact, 3) automatically create tickets in your ITSM (Jira, ServiceNow) using Nessus/Tenable APIs or a middleware script, 4) assign owners, set SLA windows (e.g., 7 days for Critical, 30 days for Medium), 5) implement fixes (patch, config change), and 6) run a verification scan to close the ticket. For small businesses without complex ITSM, export CSVs from Nessus and maintain a remediation tracker (spreadsheet or lightweight ticket tool) with columns for asset, finding, CVE/ID, remediation steps, owner, planned/actual remediation date, and verification scan timestamp. Automate evidence collection by saving HTML/PDF reports and the verification scan IDs to show auditors.
Example small-business scenario: a 50-seat engineering firm keeps CUI on a segmented file server and laptops. Deploy a Nessus scanner on the same VLAN as the file server to avoid firewall issues. Create a "CUI-Authenticated Monthly" policy with SMB and WinRM credentials (use a service account with local admin rights only on the file server) and a "Workstation Weekly" policy with LAPS-managed local admin creds. After a scan highlights two critical missing patches on the file server, open a remediation ticket, patch during the next maintenance window, then run a focused post-patch authenticated scan showing the patches are installed—retain both before/after reports as evidence for the Compliance Framework assessment.
Compliance tips and risks: always document your scan policies, credential management approach, scheduling, and remediation SLAs as part of the Compliance Framework evidence package. Tag assets that store CUI and increase scan frequency for those tags. Regularly test credentialed scans in a staging environment to ensure they do not disrupt production. The risk of not implementing RA.L2-3.11.2 properly includes undetected exploitable vulnerabilities, lateral movement opportunities for attackers, potential loss of CUI, failed audits, contract termination, and reputational/legal consequences. Small businesses are particularly exposed because a single breached host can compromise CUI across the environment.
In summary, meeting RA.L2-3.11.2 with Nessus involves designing targeted scan policies, implementing credentialed scans with least-privilege service accounts, integrating scan output into a documented remediation workflow, and keeping artifacts to demonstrate verification—practical measures that are feasible for small businesses and align with the Compliance Framework's evidence requirements.
