OpenVAS: A Comprehensive Guide to Vulnerability Assessment By Beyonddennis

1. Introduction to OpenVAS

OpenVAS, standing for Open Vulnerability Assessment System, is a powerful open-source framework designed to identify, assess, and manage security vulnerabilities within networks, systems, and applications. It serves as a cornerstone in the cybersecurity toolkit for organizations seeking to enhance their security posture without incurring the significant costs associated with commercial solutions. OpenVAS is adept at discovering known vulnerabilities, misconfigurations, and potential security weaknesses that could be exploited by malicious actors.

At its core, OpenVAS functions by conducting comprehensive scans on target systems and analyzing the results to pinpoint security issues. This process involves a plugin-based architecture, which allows for a wide range of vulnerability checks and continuous updates to its extensive database of Network Vulnerability Tests (NVTs). Its utility extends from basic vulnerability scanning to sophisticated compliance auditing, making it a versatile asset for security professionals across various industries.

2. History and Evolution: From Nessus to Greenbone

The origins of OpenVAS are deeply rooted in the history of vulnerability scanning. It began as a fork of the popular Nessus scanning tool in October 2005. This occurred after Tenable Network Security, the developers of Nessus, decided to change its license from open-source to a proprietary (closed source) model. The community-driven initiative behind OpenVAS aimed to preserve an open-source alternative for vulnerability assessment, ensuring that a powerful and freely available tool remained accessible to the public.

Since its inception, OpenVAS has undergone significant evolution, with its development being primarily driven by Greenbone Networks GmbH since 2006. Greenbone Networks transformed the original OpenVAS project from merely a scanner engine into a comprehensive vulnerability management solution. This broader framework was later rebranded as Greenbone Vulnerability Management (GVM) to reflect its expanded capabilities and the company's leading role in its development. Thus, while OpenVAS is still the name of the scanner component, it is now part of the larger GVM suite.

3. Core Functionality: Vulnerability Scanning

The primary function of OpenVAS is vulnerability scanning, which involves systematically examining networks, hosts, and applications to detect known security flaws. OpenVAS achieves this by deploying a vast array of Network Vulnerability Tests (NVTs), which are essentially scripts designed to simulate various attack techniques. These tests check for a multitude of issues, including outdated software versions, common misconfigurations, weak or default credentials, and insecure SSL/TLS configurations.

OpenVAS supports both unauthenticated and authenticated scanning. Unauthenticated scans provide an external view, akin to a black-box test, identifying weaknesses accessible from the network perimeter, such as misconfigured firewalls or exposed web servers. In contrast, authenticated scans allow OpenVAS to log into target systems using provided credentials (e.g., SSH for Linux/Unix, SMB for Windows), enabling it to perform deeper, internal security checks. This grants visibility into patch levels, locally installed software, system configurations, and even registry settings, providing a more comprehensive and accurate assessment.

4. Architecture of OpenVAS

OpenVAS operates on a client-server architecture, comprising several interconnected components that work in harmony to deliver its vulnerability scanning and management capabilities. The core components include the OpenVAS Scanner, the Greenbone Vulnerability Manager Daemon (GVMD), and the Greenbone Security Assistant (GSA). This modular design allows for flexibility and scalability, making it suitable for diverse IT environments.

The GVMD acts as the central control point, orchestrating the entire scanning process, managing scan policies, and storing results in a PostgreSQL database. It communicates with the OpenVAS Scanner using the Open Scanner Protocol (OSP). The GSA provides the web-based graphical user interface (GUI) for users to interact with the system, configure scans, review findings, and generate reports. Finally, the OpenVAS Scanner is the workhorse, responsible for executing the actual vulnerability tests against target systems, utilizing the continuously updated vulnerability feeds.

5. The Greenbone Vulnerability Management (GVM) Ecosystem

While often used interchangeably, OpenVAS is technically the scanner component within a larger suite of tools known as Greenbone Vulnerability Management (GVM). Greenbone Networks, the driving force behind OpenVAS development since 2006, created GVM to offer a complete vulnerability management solution beyond just scanning. The GVM framework encapsulates various services designed to provide a full lifecycle approach to vulnerability assessment, from initial discovery to reporting and remediation.

The GVM ecosystem includes, but is not limited to, the OpenVAS Scanner, the Greenbone Vulnerability Manager Daemon (GVMD), the Greenbone Security Assistant (GSA), and the Greenbone Community Feed (GCF). This integration of components means that GVM provides the overarching structure for managing scan tasks, users, and results, while OpenVAS specifically handles the execution of vulnerability tests. This distinction is crucial for understanding the comprehensive nature of the Greenbone offering.

6. Installation on Linux Systems

Installing OpenVAS, or more accurately the Greenbone Vulnerability Management (GVM) suite that includes OpenVAS, on Linux distributions typically involves several steps. Users generally begin by ensuring their system's package lists are updated and then installing the necessary GVM or OpenVAS packages through their distribution's package manager. For Kali Linux, a popular choice for cybersecurity professionals, commands like `sudo apt update && sudo apt upgrade -y` followed by `sudo apt install openvas -y` are common starting points.

After the initial package installation, a crucial step is to run a setup or initialization command, such as `sudo gvm-setup`, which configures the OpenVAS services and sets up essential databases. This process often involves downloading a large volume of Network Vulnerability Tests (NVTs), which can take a considerable amount of time and consume significant data. Upon completion, users are usually provided with initial admin credentials to access the web interface, and it's recommended to verify the setup's correctness using commands like `sudo gvm-check-setup`.

7. Key Components Explained: Greenbone Security Assistant (GSA)

The Greenbone Security Assistant (GSA) serves as the primary web-based graphical user interface (GUI) for interacting with the Greenbone Vulnerability Management (GVM) system, which includes OpenVAS. It is the main contact point for users, offering an intuitive way to manage and configure vulnerability scans, review scan results, and generate various reports. The GSA streamlines the user experience, making complex vulnerability assessment tasks more accessible to security analysts and operators.

Through the GSA, users can define scan targets, select scan policies, schedule scans, and access a centralized view of all IT assets and their associated vulnerabilities. Its role is critical in providing transparency and clarity over the security status of an infrastructure, visualizing complex information to help in quick decision-making. The GSA connects to the Greenbone Vulnerability Management Daemon (GVMD) via the Greenbone Security Assistant Daemon (GSAD), ensuring seamless communication and data management within the GVM framework.

8. Key Components Explained: OpenVAS Scanner

The OpenVAS Scanner is the engine room of the Greenbone Vulnerability Management (GVM) solution, directly responsible for performing the actual vulnerability assessments on target systems. It is a full-featured scan engine that executes a continuously updated and extensive feed of Vulnerability Tests (VTs), also known as Network Vulnerability Tests (NVTs). These VTs are essentially small scripts, often written in the Nessus Attack Scripting Language (NASL), which simulate various attack techniques and checks for known vulnerabilities.

The scanner's capabilities are broad, encompassing unauthenticated and authenticated testing, and supporting various high-level and low-level internet and industrial protocols. It interacts with the Greenbone Vulnerability Management Daemon (GVMD) to retrieve scan configurations and report its findings, working in conjunction with the OSPD-OpenVAS component. The effectiveness of the OpenVAS Scanner is heavily reliant on its comprehensive and regularly updated NVT feed, which ensures it can detect the latest threats and security weaknesses.

9. Key Components Explained: Greenbone Vulnerability Manager (GVMd)

The Greenbone Vulnerability Manager Daemon (GVMD), often referred to as the Greenbone Vulnerability Manager, serves as the central intelligence and control unit within the Greenbone Vulnerability Management (GVM) architecture. This daemon is the core service that elevates plain vulnerability scanning into a comprehensive vulnerability management solution. Its primary responsibilities include coordinating the entire scanning process, managing scan configurations, and storing all collected scan results and related data in a PostgreSQL database.

GVMD acts as an intermediary, controlling the OpenVAS Scanner via the Open Scanner Protocol (OSP) and providing the XML-based Greenbone Management Protocol (GMP) for interaction with the Greenbone Security Assistant (GSA). Beyond scan orchestration, GVMD also handles critical functions such as user management, including permissions control with groups and roles, and manages an internal runtime system for scheduled tasks and other events, ensuring the seamless operation of the GVM suite.

10. The Greenbone Community Feed (GCF)

The Greenbone Community Feed (GCF) is a vital component of the OpenVAS ecosystem, providing a continuously updated database of Network Vulnerability Tests (NVTs) that the OpenVAS Scanner utilizes to detect vulnerabilities. This feed is crucial for keeping OpenVAS effective against the ever-evolving landscape of cyber threats, ensuring that it can identify the latest known vulnerabilities, misconfigurations, and security weaknesses. As of January 2019, the GCF contained over 50,000 NVTs, a number that continues to grow with daily updates.

The GCF is distinguished from the commercial Greenbone Enterprise Feed, but it still offers a robust collection of vulnerability checks that are freely available and licensed under a GPL-compatible license. The regular updates to the GCF mean that OpenVAS users benefit from timely information on newly exposed vulnerabilities and Common Vulnerabilities and Exposures (CVEs), empowering them to maintain an up-to-date security posture. The community's active participation and Greenbone Networks' ongoing development ensure the feed's comprehensiveness and relevance.

11. Scan Configuration: Targets and Credentials

Configuring a scan in OpenVAS involves defining the scope of the assessment, specifically identifying the targets to be scanned. Users can specify target hosts by their IP addresses or hostnames, and can even define IP address ranges or subnets to cover entire networks. This flexibility allows organizations to tailor scans to their specific needs, whether for a single critical server or an entire enterprise network segment. The configuration process is typically managed through the Greenbone Security Assistant (GSA) web interface, making it user-friendly.

Another crucial aspect of scan configuration is the inclusion of credentials for authenticated checks. OpenVAS supports various credential types, including SSH for Linux/Unix systems, SMB for Windows systems, ESXi for VMware servers, and SNMP for network devices. Providing credentials significantly enhances the depth and accuracy of scans, allowing OpenVAS to log into target systems and perform local security checks, uncovering vulnerabilities that might be hidden from unauthenticated network-level scans, such as missing patches or insecure software configurations.

12. Scan Configuration: Scan Types and Policies

OpenVAS offers a range of scan types and policies, allowing users to customize the intensity and focus of their vulnerability assessments. These configurations determine which Network Vulnerability Tests (NVTs) are executed, the depth of the scan, and the amount of resources consumed. Standard default scan configurations are provided out-of-the-box, but users have the flexibility to create custom scan policies to align with specific security objectives or compliance requirements.

Examples of common scan types include "Full and Fast" scans, which provide a balance between thoroughness and speed, and more targeted scans focusing on specific services, ports, or vulnerability families. Users can adjust parameters such as the list of ports to scan, the safe checks preference (to avoid potentially disruptive tests), and even integrate custom Network Vulnerability Tests. This granular control ensures that assessments can be tailored to minimize impact on production systems while maximizing the effectiveness of vulnerability detection.

13. Understanding Scan Results: Severity and CVSS

After a scan is completed, OpenVAS generates detailed reports that are essential for understanding the security posture of the scanned systems. These reports highlight identified vulnerabilities, categorize them by severity, and often include recommendations for remediation. A critical aspect of interpreting these results is understanding the severity levels assigned to each vulnerability. OpenVAS, like many other vulnerability scanners, typically categorizes vulnerabilities into levels such as Low, Medium, High, and Critical.

Many of these severity ratings are derived from or aligned with the Common Vulnerability Scoring System (CVSS), an open standard for assessing the severity of computer system security vulnerabilities. CVSS provides a numerical score and a vector string that describes the characteristics and severity of a vulnerability, aiding in consistent and measurable risk assessment. By understanding the assigned severity and the underlying CVSS scores, security professionals can prioritize remediation efforts, focusing on the most impactful vulnerabilities first to minimize potential risks to their organization.

14. Reporting and Exporting Results

OpenVAS excels in its ability to generate comprehensive and customizable reports, which are crucial for communicating findings to various stakeholders, from technical teams to management and compliance auditors. These reports provide detailed insights into identified vulnerabilities, their severity, descriptions, and often include actionable remediation recommendations. The flexibility in reporting allows organizations to obtain the specific information needed for different purposes, whether for immediate technical patching or for broader strategic security reviews.

A key feature of OpenVAS is its robust export capabilities. Scan results can be exported in various formats, catering to diverse needs and integration requirements. Common export formats include XML, CSV, PDF, and HTML. The XML format is particularly useful for integration with other security tools or for further programmatic analysis, while PDF and HTML provide user-friendly, readable documents suitable for presentation and archival. Tools specifically designed for OpenVAS reporting can also merge multiple scan reports into a single, structured output, or create specialized formats like Excel spreadsheets for easy data manipulation and analysis, complete with summary sheets and vulnerability details.

15. Advanced Features: Schedules and Alerts

OpenVAS extends its utility beyond one-time scans by offering advanced features like scan scheduling and alerting mechanisms, which are vital for maintaining continuous security monitoring. The ability to schedule scans allows organizations to automate vulnerability assessments to run at specific times, such as overnight or during off-peak hours, minimizing potential disruption to active systems. These schedules can be configured for one-time future scans or for recurring assessments, like daily or weekly intervals, ensuring regular oversight of the network's security posture.

While the prompt didn't explicitly detail alert features, a comprehensive vulnerability management solution like GVM, which OpenVAS is part of, inherently supports alerting. This typically involves notifications for completed scans, detected critical vulnerabilities, or changes in scan status. Such automation ensures that security teams are promptly informed of new threats or significant findings, enabling a swift response and reducing the window of vulnerability. These features are indispensable for implementing a proactive and continuous vulnerability management program.

16. Integration with Other Tools

OpenVAS, as part of the Greenbone Vulnerability Management (GVM) suite, is designed with integration capabilities that allow it to fit seamlessly into a broader cybersecurity ecosystem. Its ability to integrate with other security tools and frameworks is crucial for organizations seeking a holistic approach to vulnerability management and overall security operations. This interoperability ensures that vulnerability data can be leveraged across different platforms for enhanced analysis, automation, and incident response.

Common integration points include Security Information and Event Management (SIEM) systems like Splunk or ELK, which can ingest OpenVAS scan reports (often in XML or CSV format) to correlate vulnerability data with event logs and alerts, providing a more comprehensive view of security incidents. OpenVAS also provides APIs (Application Programming Interfaces) for programmatic access, enabling automation of scan tasks, data extraction, and integration into custom scripts or Continuous Integration/Continuous Delivery (CI/CD) pipelines for DevOps environments.

17. Use Cases: Compliance and Auditing

OpenVAS is a highly effective tool for organizations aiming to achieve and maintain compliance with various security standards and regulatory requirements. In today's stringent regulatory landscape, demonstrating proactive vulnerability management is often a mandatory component of compliance audits. OpenVAS aids in this by systematically identifying security gaps that could lead to non-compliance with standards such as PCI DSS, HIPAA, GDPR, ISO 27001, and CIS benchmarks.

The detailed reports generated by OpenVAS, available in various formats including archivable PDFs and XML, serve as tangible proof of ongoing security assessments. These reports can be tailored for audit purposes or C-level executives, clearly outlining identified vulnerabilities, their severity, and the steps taken towards remediation. By regularly leveraging OpenVAS for compliance auditing, organizations can identify and address security weaknesses before external audits, helping to ensure adherence to industry standards and avoid potential penalties.

18. Use Cases: Penetration Testing Support

While OpenVAS is primarily a vulnerability scanner designed to identify known weaknesses, it also serves as a valuable tool in the initial phases of penetration testing. Penetration testers often use OpenVAS as part of their reconnaissance toolkit to quickly discover potential vulnerabilities in a target environment. By performing automated scans, testers can efficiently identify common misconfigurations, outdated software, and known exploits that might be present on the target systems, providing a solid foundation for more in-depth manual exploitation attempts.

OpenVAS's ability to conduct both unauthenticated and authenticated scans is particularly useful in this context. Unauthenticated scans can map out the external attack surface, while authenticated scans provide deeper insights into internal system weaknesses, mirroring what an attacker might discover if they gain initial access. Although OpenVAS does not replace the nuanced and creative aspects of manual penetration testing, it significantly streamlines the information gathering phase, allowing testers to focus their efforts on validating and exploiting critical findings identified by the scanner.

19. Strengths and Limitations of OpenVAS

OpenVAS offers several significant strengths that make it a popular choice for vulnerability assessment. Its primary advantage is its open-source and free nature, making it a cost-effective solution for organizations of all sizes, particularly small businesses or those with limited budgets. It boasts a comprehensive and continuously updated database of Network Vulnerability Tests (NVTs), ensuring it can detect a wide range of known vulnerabilities. The tool is also highly customizable, allowing users to tailor scan policies and integrate it with other security tools, enhancing its flexibility and adaptability within diverse IT environments. Its user-friendly web interface (GSA) simplifies the management of scans and results.

However, OpenVAS also has certain limitations. One notable drawback is its resource intensity; active scans can consume significant CPU and RAM, requiring dedicated server resources for optimal performance. Like any automated scanner, it can sometimes produce false positives (reporting vulnerabilities that don't truly exist) or false negatives (missing actual vulnerabilities), requiring manual verification of results. While powerful, some argue that its vulnerability coverage might be less extensive than certain commercial scanners like Nessus in specific areas, particularly for remote checks of high and critical vulnerabilities, though the Greenbone Enterprise Feed aims to address this for commercial users. OpenVAS also has a learning curve, especially for complex setups and interpreting results.

20. Future Trends and Community Impact

The future of OpenVAS, as an integral part of the Greenbone Vulnerability Management (GVM) ecosystem, appears strong, driven by continuous development from Greenbone Networks and a vibrant open-source community. The ongoing expansion of the Greenbone Community Feed (GCF) with new Network Vulnerability Tests (NVTs) ensures that OpenVAS remains relevant and capable of detecting emerging threats and vulnerabilities. As cyber threats evolve in sophistication, the framework's ability to adapt and incorporate new scanning techniques and protocols will be key to its sustained impact.

The open-source nature of OpenVAS fosters a broad community of security experts and developers who contribute to its improvement, provide support, and report issues like false positives, ensuring prompt feedback and knowledge sharing. This community-driven approach enhances the tool's transparency, reliability, and security. As organizations increasingly prioritize proactive cybersecurity measures and continuous monitoring, tools like OpenVAS, offering a powerful and cost-effective solution for vulnerability assessment, will continue to play an essential role in safeguarding digital assets and ensuring compliance in an ever-changing threat landscape. The potential for further integration with modern security workflows, such as CI/CD pipelines and cloud environments, indicates its continued evolution and relevance.