Nessus Vulnerability Scanner: A Comprehensive Guide to Network Security Assessments

Explore the capabilities and applications of the Nessus vulnerability scanner. This guide provides an overview of Nessus's functionality, its role in identifying security vulnerabilities, and best practices for using Nessus for effective penetration testing and network security assessments.

Nessus Vulnerability Scanner: A Comprehensive Guide

Introduction to Nessus

Nessus is a popular vulnerability scanner developed by Tenable, Inc. It's a subscription-based service (Tenable.io and Nessus Cloud) that helps identify security vulnerabilities in computer systems and networks. While now primarily a commercial product, Nessus has its roots in open-source software, using the Common Vulnerabilities and Exposures (CVE) architecture for consistent reporting.

Nessus helps in penetration testing and vulnerability assessments, identifying weaknesses that could be exploited by malicious actors. It works by probing systems, identifying running services on each port, and then checking for known vulnerabilities in those services.

How Nessus Works

Nessus and similar scanners understand how network services (web servers, email servers, file transfer servers, etc.) communicate. Data is typically sent using TCP streams with higher-level protocols. To manage multiple connections, computers divide their network connections into "ports."

Nessus examines these ports and services, looking for:

Security flaws that could allow unauthorized access to data.
Misconfigurations (e.g., open mail relays).
Denial-of-service (DoS) vulnerabilities.
Weak or default passwords.
Software bugs, missing patches, and other issues.

Nessus supports various operating systems (Windows, Linux, Unix, etc.) and applications.

Nessus's Open Source History

Originally an open-source project (created by Renaud Daraison in 1998), Nessus transitioned to a closed-source, commercial license in 2005 under Tenable Network Security. The free, open-source aspects allowed for community contributions and transparency.

Nessus Essentials and Plugins

Nessus Essentials is a free version with limited features. Nessus uses plugins to extend its capabilities. Plugins can perform various tasks, such as:

Identifying operating systems and services on specific ports.
Detecting vulnerabilities in software components (FTP, SSH, SMB, etc.).
Checking for compliance with security standards.

Performing a Vulnerability Scan with Nessus

A Nessus scan involves several steps:

Initial Scan Setup: Configure the scan parameters (ports to scan, plugins to enable, policies).
Select Scan Template: Choose a pre-defined scan template to simplify the process.
Port Scanning: Nessus scans the specified ports on each host.
Service Detection: Identifies the services running on each port.
Operating System Detection: Determines the operating system of each host.
Vulnerability Check: Compares the discovered services and operating systems against a database of known vulnerabilities.

Key Advantages of Nessus

Accuracy: Nessus doesn't rely on guesswork; it thoroughly checks systems.
Regular Updates: The vulnerability database is frequently updated.
Extensibility: Supports scripting and plugins for customized scans.
Open Source (Essentials): A free version is available.
Patching Assistance: Often provides recommendations for fixing vulnerabilities.
Ease of Use: Designed with security professionals in mind for intuitive operation.
Cross-Platform Compatibility: Can run on various platforms.

Nessus Agents

Nessus Agents are small programs installed on individual hosts. They provide more detailed system information, vulnerability data, and compliance information to the Nessus management console. They're particularly useful for endpoints and devices with intermittent internet connectivity.

Nessus: Versions and Capabilities

Nessus Agents

Nessus Agents are lightweight programs installed directly onto individual computers or servers. They collect system information, vulnerability data, and compliance details, sending this data to the Tenable.io platform for analysis. This approach improves the flexibility and coverage of scans, especially for devices with intermittent internet connectivity. Agents work with various operating systems (Windows, macOS, Linux) and device types (desktops, laptops, virtual machines).

Nessus Professional

Nessus Professional automates vulnerability assessments, quickly identifying and prioritizing issues such as software flaws, missing patches, malware, and misconfigurations across various operating systems, endpoints, and applications. It offers comprehensive vulnerability detection for a single price, providing unlimited scans. Its key features include:

Fast, accurate vulnerability scanning.
Prioritization of critical vulnerabilities.
Mobile vulnerability assessment capabilities.
Easy policy creation and network-wide scanning.

Nessus Manager

Nessus Manager extends the capabilities of Nessus Professional by adding robust management and collaboration features to reduce your organization's attack surface. Key integrations include:

Patch Management: Integrates with solutions from IBM, Microsoft, Red Hat, and Dell to streamline patching.
Mobile Device Management (MDM): Works with MDM solutions from Microsoft, Apple, and others to incorporate mobile devices into vulnerability management.

Tenable.io

Tenable.io is a cloud-based, subscription service providing comprehensive vulnerability management. Leveraging Nessus technology, it offers extensive vulnerability coverage and prioritization recommendations. Key features include:

Centralized reporting and management for large teams.
Advanced vulnerability analysis and reporting.
Remote scan scheduling and policy management.
Management of multiple Nessus scanners.

Conclusion

Nessus remains a leading vulnerability scanning and management solution. Its various versions (Agents, Professional, Manager, and Tenable.io) offer a range of capabilities to meet the needs of organizations of all sizes.