--- name: scanning-infrastructure-with-nessus-3934ae92b2f8 description: Tenable Nessus is the industry-leading vulnerability scanner used to identify security weaknesses across network infrastructure including servers, workstations, network devices, and operating systems. domain: cybersecurity subdomain: vulnerability-management tags: - vulnerability-management - cve - nessus - tenable - infrastructure-scanning - risk version: '1.0' author: Krishna Kumar (xalgord) license: Apache-2.0 nist_csf: - ID.RA-01 - ID.RA-02 - ID.IM-02 - ID.RA-06 --- # Scanning Infrastructure with Nessus ## Overview Tenable Nessus is the industry-leading vulnerability scanner used to identify security weaknesses across network infrastructure including servers, workstations, network devices, and operating systems. This skill covers configuring scan policies, running authenticated and unauthenticated scans, interpreting results, and integrating Nessus into continuous vulnerability management workflows. ## When to Use - When conducting security assessments that involve scanning infrastructure with nessus - When following incident response procedures for related security events - When performing scheduled security testing or auditing activities - When validating security controls through hands-on testing ## Detection Gaps & Validation - **Unauthenticated-only scans** — miss 45-60% of vulns. Validate credentials with plugin 19506 (Scan Information) showing authenticated checks ran. - **Host discovery gaps** — hosts not answering the ping method are skipped. Validate the scanned-host count against the expected target range. - **Excluded fragile systems** — SCADA/medical exclusions become blind spots; validate they're covered by a safe policy rather than dropped. - **Stale plugins** — validate plugins updated before each scan so recent CVEs are tested. - **Plugin tuning false positives** — validate critical findings manually before escalating. - **Network reachability** — firewall rules between scanner and target cause silent misses; validate connectivity to management ports first. ## Prerequisites - Nessus Professional or Essentials license installed and activated - Network access to target systems (firewall rules allowing scanner IP) - Administrative credentials for authenticated scanning - Understanding of TCP/IP networking and common services - Written authorization for scanning target environments ## Core Concepts ### Nessus Architecture Nessus operates as a client-server application where the Nessus scanner engine runs as a service (nessusd) on the host system. It uses a plugin-based architecture with over 200,000 plugins updated weekly by Tenable's research team. Each plugin tests for a specific vulnerability, misconfiguration, or compliance check. ### Scan Types 1. **Host Discovery** - Identifies live hosts using ICMP, TCP, UDP, and ARP 2. **Basic Network Scan** - Default policy covering common vulnerabilities 3. **Advanced Scan** - Custom policy with granular plugin selection 4. **Credentialed Patch Audit** - Authenticated scan checking installed patches 5. **Web Application Tests** - Scans for web-specific vulnerabilities 6. **Compliance Audit** - Checks against CIS, DISA STIG, PCI DSS benchmarks ### Plugin Families Nessus organizes plugins into families including: - **Operating Systems**: Windows, Linux, macOS, Solaris - **Network Devices**: Cisco, Juniper, Palo Alto, Fortinet - **Web Servers**: Apache, Nginx, IIS, Tomcat - **Databases**: Oracle, MySQL, PostgreSQL, MSSQL - **Services**: DNS, SMTP, FTP, SSH, SNMP ## Workflow ### Step 1: Initial Configuration ```bash # Start Nessus service sudo systemctl start nessusd sudo systemctl enable nessusd # CLI management with nessuscli /opt/nessus/sbin/nessuscli update --all /opt/nessus/sbin/nessuscli fix --list # Verify plugin count /opt/nessus/sbin/nessuscli update --plugins-only ``` ### Step 2: Create Scan Policy Configure a custom scan policy through the Nessus web UI at https://localhost:8834: 1. Navigate to Policies > New Policy > Advanced Scan 2. Configure General settings: name, description, targets 3. Set Discovery settings: - Host Discovery: Ping methods (ICMP, TCP SYN on ports 22,80,443) - Port Scanning: SYN scan on common ports or all 65535 ports - Service Discovery: Probe all ports for services 4. Configure Assessment settings: - Accuracy: Override normal accuracy (reduce false positives) - Web Applications: Enable if scanning web servers 5. Select Plugin families relevant to target environment ### Step 3: Configure Credentials For authenticated scanning, configure credentials under the Credentials tab: - **SSH**: Username/password or SSH key pair - **Windows**: Domain credentials via SMB, WMI - **SNMP**: Community strings (v1/v2c) or USM credentials (v3) - **Database**: Oracle, MySQL, PostgreSQL connection strings - **VMware**: vCenter or ESXi credentials ### Step 4: Run the Scan ``` # Using Nessus REST API via curl # Authenticate and get token curl -k -X POST https://localhost:8834/session \ -d '{"username":"admin","password":"password"}' \ -H "Content-Type: application/json" # Create scan curl -k -X POST https://localhost:8834/scans \ -H "X-Cookie: token=" \ -H "Content-Type: application/json" \ -d '{ "uuid": "", "settings": { "name": "Infrastructure Scan Q1", "text_targets": "192.168.1.0/24", "enabled": true, "launch": "ON_DEMAND" } }' # Launch scan curl -k -X POST https://localhost:8834/scans//launch \ -H "X-Cookie: token=" # Check scan status curl -k -X GET https://localhost:8834/scans/ \ -H "X-Cookie: token=" ``` ### Step 5: Analyze Results Nessus categorizes findings by severity: - **Critical (CVSS 9.0-10.0)**: Immediate remediation required - **High (CVSS 7.0-8.9)**: Remediate within 7-14 days - **Medium (CVSS 4.0-6.9)**: Remediate within 30 days - **Low (CVSS 0.1-3.9)**: Remediate during next maintenance window - **Informational**: No immediate action required ### Step 6: Export and Report ```bash # Export via REST API curl -k -X POST "https://localhost:8834/scans//export" \ -H "X-Cookie: token=" \ -H "Content-Type: application/json" \ -d '{"format":"nessus"}' # Supported formats: nessus (XML), csv, html, pdf ``` ## Best Practices 1. Schedule scans during maintenance windows to minimize production impact 2. Use authenticated scanning for 45-60% more vulnerability detection 3. Exclude fragile systems (medical devices, legacy SCADA) from aggressive scans 4. Maintain separate scan policies for different network segments 5. Update plugins before every scan to catch recently disclosed CVEs 6. Validate critical findings manually before escalating to remediation teams 7. Implement scan result trending to track remediation progress over time 8. Store scan results in Tenable.sc or Tenable.io for centralized management ## Common Pitfalls - Running unauthenticated scans only (misses 45-60% of vulnerabilities) - Scanning without written authorization (legal and ethical violations) - Ignoring scan performance impact on production systems - Failing to tune plugins leading to excessive false positives - Not validating scanner network connectivity before launching scans - Using default scan policies without customization for the environment ## Related Skills - performing-authenticated-vulnerability-scan - prioritizing-vulnerabilities-with-cvss-scoring - implementing-continuous-vulnerability-monitoring - performing-network-vulnerability-assessment --- Source attribution: xalgord Original project: https://github.com/xalgord/xalgorix/blob/cec44d71b1d998208e1e2091982d0ee2f928041f/internal/tools/skills/data/vulnerability-management/scanning-infrastructure-with-nessus/SKILL.md License: Apache-2.0 License information: https://www.apache.org/licenses/LICENSE-2.0 Original upstream instructions; downloaded from Mega AI Hub. ## Upstream license notice Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. 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See the License for the specific language governing permissions and limitations under the License. # Mega AI Hub resource metadata Creator / publisher: xalgord Original project: https://github.com/xalgord/xalgorix/blob/cec44d71b1d998208e1e2091982d0ee2f928041f/internal/tools/skills/data/vulnerability-management/scanning-infrastructure-with-nessus/SKILL.md Attribution basis: Source repository record Fields of work: Development & Engineering Roles: DevOps / SRE, QA / Test Engineer, Security Engineer Specialties: DevOps, Testing Tools: Nessus Country applicability: Country not specified Classification basis: Source catalog labels Instruction SHA-256: e7bff597e0881f22a9a7145ed1c308945321809c43ef9a6e45454fd9962dafd7