Vulnerability Scanning with Nessus for Penetration Testing

Vulnerability Scanning with Nessus for Penetration Testing

Vulnerability scanning and penetration testing are two distinct yet interrelated practices in the realm of cybersecurity. 

Buy Now

Vulnerability scanning identifies, assesses, and reports on the vulnerabilities within a network or system. It is often automated and seeks out weak points that could be exploited by malicious actors. Penetration testing, or "pen testing," on the other hand, involves actively exploiting those vulnerabilities to determine the extent of damage or unauthorized access that could be achieved by attackers. While vulnerability scanning primarily focuses on detection, penetration testing goes a step further by attempting to breach the system.

Nessus is one of the most widely used tools for vulnerability scanning in the cybersecurity industry. Developed by Tenable, it has become a de facto standard for identifying security flaws in a wide range of systems. When used as part of a penetration testing engagement, Nessus provides an invaluable baseline for discovering and understanding potential vulnerabilities before they can be actively exploited.

What is Nessus?

Nessus is a vulnerability scanner designed to automate the process of finding known vulnerabilities in systems, devices, and applications. It uses a combination of plugins—software components that contain the logic to detect vulnerabilities—and regular updates to stay current with the latest threats. The scanner can identify issues such as:

• Misconfigurations
• Outdated or vulnerable software versions
• Open ports and services
• Missing patches
• Known exploits

Nessus provides detailed reports and remediation suggestions, making it an essential tool for system administrators, security analysts, and penetration testers alike.

Role of Nessus in Penetration Testing

Penetration testing involves multiple phases: reconnaissance, scanning, gaining access, maintaining access, and covering tracks. Nessus comes into play primarily during the scanning phase. The role of Nessus is to perform comprehensive vulnerability assessments, allowing penetration testers to focus their efforts on known weaknesses, thereby improving efficiency and accuracy.

While Nessus does not perform the actual exploitation (this is typically done using tools like Metasploit), it plays a crucial role in:

1. Identifying Attack Vectors: Nessus helps pinpoint vulnerabilities that could be used as attack vectors during an engagement. These could include outdated software, unpatched systems, or misconfigurations that an attacker could exploit.

2. Prioritizing Threats: Vulnerability scanners like Nessus categorize vulnerabilities by severity (e.g., low, medium, high, critical), enabling penetration testers to prioritize their efforts based on potential risks. This is especially important in larger environments where the sheer volume of vulnerabilities can be overwhelming.

3. Reporting and Documentation: One of the final steps in penetration testing involves delivering a comprehensive report to the organization. Nessus provides detailed output, including vulnerability descriptions, affected systems, and remediation recommendations. This helps penetration testers convey the findings in a way that technical teams can easily understand and act upon.

How Nessus Works

Nessus uses a multi-step process to scan for vulnerabilities:

1. Discovery: Nessus first performs a discovery scan to identify live hosts, open ports, and running services within the network. This helps create an initial map of the target environment.

2. Assessment: Once the discovery scan is complete, Nessus checks the detected systems against its library of plugins. These plugins contain checks for specific vulnerabilities, misconfigurations, and known security flaws. Nessus cross-references the system's characteristics (e.g., operating system version, open ports) against its database and looks for potential issues.

3. Analysis and Reporting: After the scan is completed, Nessus provides a detailed report on the identified vulnerabilities, their severity levels, and recommendations for fixing them. Reports can be customized, filtered, and exported in various formats like HTML, CSV, or PDF.

Setting Up Nessus for Vulnerability Scanning

Before using Nessus in a penetration test, it’s essential to configure the tool properly:

1. Install Nessus: Nessus can be installed on a variety of platforms including Windows, Linux, and macOS. Tenable provides a setup guide tailored to each platform.

2. Create a Scan Policy: Scan policies define how Nessus scans a target. They allow the user to customize settings like scan depth, types of vulnerabilities to look for, and network behavior (e.g., stealth scanning, speed). Nessus offers pre-built templates, such as "Basic Network Scan" or "Advanced Scan," which users can further customize based on their objectives.

3. Define Scan Targets: After configuring a scan policy, the next step is defining the target. In the context of penetration testing, targets could range from a single system to an entire subnet or organization’s network. Nessus supports both IP addresses and hostnames.

4. Run the Scan: Once the scan is configured and the targets are set, Nessus begins the scanning process. The duration depends on the scope of the target and the complexity of the scan policy. During the scan, Nessus performs various checks to determine potential vulnerabilities.

5. Review Results: After the scan is complete, Nessus generates a report that details the vulnerabilities found. These reports are typically organized by severity and affected hosts, making it easy for penetration testers to prioritize their focus.

Types of Nessus Scans for Penetration Testing

Nessus provides different types of scans that can be tailored to a penetration testing engagement:

1. Network Scan: This is the most basic type of scan, designed to identify vulnerabilities in network services. It scans for open ports, identifies the services running on those ports, and checks them against a list of known vulnerabilities.

2. Web Application Scan: Nessus can also be configured to look for vulnerabilities in web applications. This includes checks for common web application vulnerabilities such as SQL injection, cross-site scripting (XSS), and insecure authentication mechanisms.

3. Credentialed vs. Non-Credentialed Scans: A credentialed scan uses valid credentials (such as SSH or Windows Admin credentials) to perform a deeper scan of the target system. This allows Nessus to detect more vulnerabilities because it has access to the internal configuration of the system. Non-credentialed scans, on the other hand, are limited to what can be detected from the outside without authentication.

4. Compliance Scans: Nessus can be used to verify that systems meet certain compliance standards, such as PCI-DSS, HIPAA, or CIS benchmarks. These scans help organizations ensure that their systems are configured in accordance with industry standards.

Best Practices for Using Nessus in Penetration Testing

While Nessus is a powerful tool, it’s important to use it correctly to maximize its effectiveness during a penetration test. Below are some best practices to keep in mind:

1. Run Credentialed Scans: Credentialed scans provide a more accurate picture of the vulnerabilities in a system since they have access to internal settings and configurations. Always attempt to run credentialed scans where possible.

2. Update Plugins Regularly: Nessus relies on its plugin database to identify vulnerabilities. Ensure that Nessus plugins are updated regularly to stay current with the latest threats and vulnerabilities.

3. Use Multiple Scan Policies: Different scan policies may yield different results. For instance, a basic network scan might miss web application vulnerabilities. Use multiple scan types to get a comprehensive view of the target.

4. Cross-Reference Results: Nessus is not the only vulnerability scanner available. Cross-reference its results with other tools like OpenVAS, Nmap, or Burp Suite to ensure nothing is missed.

5. Correlate with Manual Testing: While Nessus automates vulnerability detection, manual testing is still necessary for more complex attacks. Use Nessus to gather initial data, but complement it with manual penetration testing techniques.

Conclusion

Vulnerability scanning with Nessus plays an integral role in penetration testing by streamlining the identification and prioritization of potential weaknesses in a system or network. While it does not replace the need for manual testing and exploitation, Nessus provides a strong foundation upon which penetration testers can build. By identifying vulnerabilities, categorizing them by severity, and offering remediation suggestions, Nessus enables security professionals to focus their efforts on critical issues and helps organizations strengthen their overall security posture.

SC-400: Microsoft Info Protection Admin Practice Test " Udemy