This post provides a practical, implementation-focused checklist to harden publicly accessible information systems in order to satisfy FAR 52.204-21 basic safeguarding requirements and CMMC 2.0 Level 1 control AC.L1-B.1.IV, with concrete technical steps, small-business scenarios, and compliance tips you can act on immediately.
Why this matters (Compliance Framework context)
FAR 52.204-21 requires contractors to apply basic safeguarding to systems that process, store, or transmit federal contract information (FCI); CMMC 2.0 Level 1 maps to these basic cyber hygiene practices and expects demonstrable controls for publicly accessible systems. For the Compliance Framework audience this means you must show documented, repeatable configuration and operational controls for internet-facing assets (websites, APIs, mail servers, remote access) so reviewers can verify protections against unauthorized access and data disclosure.
Implementation checklist — discovery, segmentation, and inventory
Begin with an accurate inventory and exposure map: list every publicly accessible host, URL, IP, and service. Use discovery tools and simple commands: nmap -sS -sV -p- example.com to enumerate open ports and services; ss -tulnp or netstat -tuln on hosts to confirm listening services. Record which systems handle FCI or contractor-sensitive information. Apply network segmentation: place public systems in a DMZ or separate VPC/public subnet with restrictive security group rules, and use ACLs or firewall rules to prevent lateral access to internal networks.
Configuration hardening and baseline builds
Create and enforce hardened baselines using CIS Benchmarks (or equivalent Compliance Framework templates) for OS and application layers. Actions include: disable unused services, lock down file permissions, run web servers as non-root users, and set secure TLS ciphers with TLS 1.2+ only. Example nginx/tls tips: set server_tokens off; add security headers (X-Frame-Options: DENY, X-Content-Type-Options: nosniff, Content-Security-Policy); and generate a strong TLS profile using Mozilla SSL Configuration Generator. Test TLS with openssl s_client -connect example.com:443 -servername example.com and verify headers with curl -I https://example.com.
SSH and admin access specifics
Harden remote admin access: require key-based SSH and disable password logins and root access in /etc/ssh/sshd_config (PermitRootLogin no, PasswordAuthentication no). If you allow SSH from the internet, restrict it to a jump/bastion host and limit source IPs where possible. Example firewall commands for a small Linux VPS: apt update && apt upgrade -y; ufw allow 80/tcp; ufw allow 443/tcp; ufw allow from 203.0.113.0/24 to any port 22 proto tcp; ufw enable. For cloud, use security groups and identity-based access (IAM) instead of long-lived credentials.
Edge defenses, WAFs, and rate limiting
Deploy perimeter protections appropriate to your hosting model: use a managed WAF (AWS WAF, Cloudflare, Azure Front Door) or mod_security for self-hosted apps to block OWASP Top Ten vectors and bots. Use CDN rate-limiting and DDoS protection for public endpoints. Configure logging for WAF and edge services and forward logs to a central collector (CloudWatch, ELK, or a SaaS SIEM) so you can demonstrate monitoring and incident detection capability to auditors.
Vulnerability management and testing
Implement a patch and vulnerability management process: schedule automated OS/application updates (weekly for critical updates), run container/image scanning (trivy), and perform authenticated vulnerability scans every quarter (OpenVAS, Nessus) plus application scans (OWASP ZAP, Nikto). Example: add a weekly cron that runs unattended-upgrades on Debian/Ubuntu or run apt update && apt upgrade -y in a controlled maintenance window. Record scan results, remediation tickets, and re-scan evidence for compliance documentation.
Small business scenarios — realistic options
Scenario A (small business using managed cloud static site): host marketing sites as S3 static sites behind CloudFront, enforce HTTPS, use AWS WAF for simple rule sets, restrict API endpoints to authenticated backends, and enable CloudFront logging + S3 access logs. Scenario B (small business running a VPS-hosted CMS): lock down SSH with keys and IP restrictions, use UFW to allow only 80/443 (ufw allow 80,443; ufw enable), install mod_security or fail2ban, keep CMS and plugins updated, and run weekly vulnerability scans. Both approaches can meet FAR/CMMC requirements if you document controls, patch cadence, and monitoring.
Compliance tips, evidence collection, and risks of non-implementation
Document configuration baselines, change control approvals, and operational procedures (patching, logging, incident response). Collect evidence: screenshots of firewall/security group settings, export of vulnerability scan reports, access logs showing blocking actions, and policy documents stating retention periods. Risks of not implementing these controls include accidental disclosure of FCI, successful exploitation (RCE, data exfiltration), contract noncompliance leading to loss of contracts or exclusion from bids, regulatory penalties, and reputational harm. Even for small businesses the cost of a breach—remediation, forensics, lost revenue—often exceeds the cost of basic hardening.
Summary: Harden publicly accessible systems by inventorying assets, segmenting networks, applying CIS-equivalent baselines, enforcing strong authentication and TLS, deploying edge protections (WAF/CDN), running routine vulnerability scans and patching, and documenting all controls and evidence. Start with small, incremental steps (inventory → baseline → logging → scanning) and you'll be able to demonstrate to auditors that your publicly accessible systems meet FAR 52.204-21 and CMMC 2.0 Level 1 expectations under the Compliance Framework.
