How does Nessus perform vulnerability assessments

Question

Nessus scans systems for known vulnerabilities using a database of plugins. How does it detect, assess, and report security issues?

Answer 1

​Nessus, developed by Tenable, is a widely used vulnerability scanner that identifies and assesses security weaknesses across various systems and networks. Here's an in-depth look at how Nessus operates:

Detection: How Nessus Identifies Vulnerabilities?

1. Target Discovery

   • Nessus initiates scans by identifying active hosts within the specified IP range.​

   • It performs port scanning to determine open ports and services running on each host.​

2. Service and OS Fingerprinting

   • Utilizes techniques to determine the operating system and services running on the target systems.​

   • This information helps tailor the vulnerability checks to the specific environment.​

3. Vulnerability Checks via Plugins

   • Nessus employs a vast library of plugins, each designed to detect specific vulnerabilities.​

   • Plugins are written in the Nessus Attack Scripting Language (NASL), allowing for detailed and customizable checks.​

   • These plugins are regularly updated to include the latest vulnerability information.​

4. Authenticated vs. Unauthenticated Scans

   • Authenticated Scans: Nessus uses provided credentials to log into systems, allowing for a comprehensive assessment of vulnerabilities, including those not exposed to the network.​

   • Unauthenticated Scans: Assess vulnerabilities that are visible without logging into the system, providing a view similar to that of an external attacker.​

Assessment: Evaluating Detected Issues

• Severity Classification

  • Each identified vulnerability is assigned a severity level based on the Common Vulnerability Scoring System (CVSS), ranging from Low to Critical.​

• Detailed Analysis

  • For each vulnerability, Nessus provides:​

    • A description of the issue.

    • Potential impact and exploitability.

    • Affected systems and services.

    • Remediation recommendations.

Reporting: Communicating Findings

• Comprehensive Reports

  • Nessus generates detailed reports that include:​

    • Lists of identified vulnerabilities.

    • Affected hosts and services.

    • Severity levels and CVSS scores.

    • Remediation steps and references.

• Customizable Output

  • Reports can be tailored to different audiences, from technical teams to executive summaries.​

  • Available in various formats, including HTML, PDF, and CSV.​

Use Case Example: Web Server Assessment

Scenario: An organization wants to assess its web server for vulnerabilities.​

Process:

1. Scan Configuration

   • Set up a Nessus scan targeting the web server's IP address.

   • Choose a scan template suitable for web applications.

2. Execution

   • Launch the scan, allowing Nessus to perform service discovery and vulnerability checks.​

3. Analysis

   • Review the generated report to identify vulnerabilities such as outdated software versions, misconfigurations, or known exploits.​

4. Remediation

   • Implement recommended fixes, such as applying patches or adjusting configurations.​

Continuous Improvement

• Regular Scanning

  • Schedule periodic scans to ensure ongoing security posture assessment.​

• Integration with Security Tools

  • Nessus can integrate with other security solutions, such as SIEM systems, to enhance threat detection and response capabilities.​

By systematically detecting, assessing, and reporting vulnerabilities, Nessus serves as a critical tool in an organization's cybersecurity arsenal, enabling proactive identification and remediation of security risks.