Getting Started with Nessus

What is Nessus?

Nessus by Tenable is a popular open-source Kali Linux program used by penetration testers. Many different security patches are offered using it. There are thousands of built-in penetration testing tools available. Nessus offers a penetration tester a plethora of tools that can help with the engagement, including:

• Locating both local and remote weaknesses
• Audits of compliance and configuration
• Examining default credentials
• Examining web applications

As a pen-tester, you should know what is Nessus and how to commonly use this program to check a server or website for potential vulnerabilities.

Prerequisites

The following prerequisites must be met to proceed with this lesson.

1. Access to a Kali Linux system with internet connectivity at the administrative, or "root," level. Tenable's hardware guidelines state that the following minimum system requirements should be met:
   • CPU: four 2GHz cores
   • RAM Memory: 4 Gigabytes (`8 GB RAM recommended)
   • Disk Space: 30 GB, not counting host operating system space The virtual machine (VM) utilized in this study runs on VMware Workstation Player and is a 64-bit version of Kali Linux (version 2020.4).
2. Access to a browser that is Nessus-compatible. According to Tenable's specifications for software, Nessus supports the following browsers:
   • `Google Chrome
   • Apple Safari
   • `Mozilla Firefox
   • `Internet Explorer
3. Obtain the Nessus activation code: Before beginning the installation procedure, Tenable advises that you get the Activation Code as Nessus cannot be configured without it. Tenable offers 3 versions of its Nessus Vulnerability Scanner: Nessus Expert, Nessus Professional, and Nessus Essentials. Although Nessus Essentials is free, it offers fewer features than its premium siblings, Nessus Professional and Nessus Expert.

For this lesson, Nessus Essentials will be used. Although the program is free, it does need a working activation code, as explained below.

1. Go to the Nessus Essentials Product Portal by clicking on https://www.tenable.com/products/nessus/activation-code

2. Your First Name, Last Name, and Email Address must be entered into the entry form.

3. To finish registering, hit the Register button.

4. Tenable will give you a confirmation once your registration has been successful. A thank-you message will then be displayed to you. 5. Check your email right away; you should see an activation code that looks like D234-C7CB-04AF-79A6-1555. If the registration email does not appear in your inbox, be sure to check your trash mail !

Installing and Configuring Nessus

Before installing Nessus, you must ensure that your setup meets the minimum system requirements.

Since Kali does not come with Nessus installed by default, you must first download the Nessus software package.

Download Nessus Package File on Kali Linux

Open a compatible web browser after starting the Kali Linux operating system. To get the required Nessus installation files, follow the instructions listed below.

1. Go to the Nessus downloads webpage.
2. Nessus is compatible with a variety of architectures and operating systems. Depending on your system requirements and setup, download the appropriate installation package.
3. When asked, check the License Agreement and click Agree after clicking the download link.

Once the download is finished, it's time to check the installation package's integrity.

Verify the Nessus Package Integrity

When you download a file from a third party, such as a vendor website, verifying file integrity becomes much more crucial. Compare the computed hash of the downloaded Nessus installation package to the file's reported checksum, as shown below.

1. On your Kali Linux desktop, you can launch a Terminal by right-clicking anywhere and choosing Open Terminal Here.
2. Get the SHA256 hash from the downloads page by clicking the Checksum link.
3. A popup window displaying an MD5 and SHA256 hash value will appear. Write down the SHA256 value.

Replace "checksum hash" with the SHA256 hash given on the download URL. Use an absolute path to swap out the path below with the location of your download.

Do not install the program if the output of your command does not imply that your installation package is valid.

Installing Nessus on Kali Linux

It is now time to install the Nessus program after you have confirmed the integrity of the package. As seen below, provide the downloaded installation package to the Debian Package Manager (pkg) utility using the I (install) argument.

The Nessus Vulnerability Scanner has just been set up on your Kali Linux operating system.

Starting And Enabling the Nessus Service

It is necessary to activate the nessusd system service before utilizing the Nessus application. Please follow the instructions below to start the nessusd service.

On your Kali Linux desktop, launch a terminal. Use the following command to launch the nessusd service:

By executing the following command, you can confirm that the service is active. The anticipated output should be Active: active (running)

To make the nessusd service run when the Kali Linux operating system boots, enter the following command.

Create and Configure scans

Nessus is currently operational thanks to your efforts. It's time to test this useful tool's capabilities for vulnerability discovery. This section's remaining instructions explain how to set up and run a scan against your Kali Linux system.

Creating a Scan

Nessus is now ready for use after installation and launch, so you can begin scanning. You must first make a scan. You may make a scan by:

• Select Scans from the top navigation bar.`
• Select "New Scan" from the menu in the top-right corner of the My Scans page.

Choose a Scan Template

Then select the desired scan template you wish to use. By identifying which parameters are programmable and how they may be changed, scan templates make the process easier. The Nessus User Guide's Scan and Policy Settings section contains a thorough overview of all the choices.

A scan policy is a predetermined collection of setup choices for running a scan. When you create a scan, you may use the newly created policy as a template in the User Defined tab. Refer to the Nessus User Guide for further details.

Configure Scan Settings

Configure the options offered by your chosen template to prepare your scan. The Basic Network Scan template comes with several default parameters already set up, making it simple for you to immediately run your first scan and check the findings. Run a fundamental scan by following these steps:

1. Make the necessary adjustments to the Basic Settings section as per your needs.

The following are the default settings:

2. Complete the remaining configurations and credentials. Though the other options may be left at their pre-configured defaults, Tenable advises checking the Discovery, Assessment, Report, and Advanced settings to make sure they are suitable for your environment.

Credentials can be configured for a scan as an option. This enables certified scans to work, which can deliver far more comprehensive data and a more detailed analysis of the risks in your environment.

Launch the Scan

After finalizing all your options, you have the option to conduct the scan right now or later by clicking the Save button. Click the down arrow, then choose Launch to start the scan right now. It will also be saved when the scan is launched.

View and Analyze Scan Results

You may learn more about the security posture and weaknesses within your company by looking at scan findings. You may choose how you view the results from your scan thanks to adjustable display choices and color-coded indications`.

The following perspectives are available for viewing scan results:

Viewing scan findings based on vulnerabilities provides insight into possible threats to your assets.

Follow these procedures to see vulnerabilities:

1. Select Scans from the top navigation bar.
2. Select the scan whose findings you wish to see.
3. pick one of the following:
   • To display vulnerabilities discovered on a single host, click the host's name.
   • To see every vulnerability, click the Vulnerabilities tab.
4. (Optional) Click a column header row's property to arrange the vulnerabilities according to that column.
5. When you click on a vulnerability row, you'll be sent to the vulnerability details page, which displays plugin details and results for each instance on a host.

Refine Nessus Settings

To examine certain scan results, search or apply filters. Using a variety of filters, you may narrow down the hosts and vulnerabilities you're interested in as well as design thorough and unique scan result screens.

Discovering Hosts:

1. Select the Hosts tab from the scan results.
2. Enter text to filter for hostname matches in the Search Hosts box located above the host's table. Nessus selects the results for you as you write based on the text you enter.

Discovering Vulnerabilities

1. Pick one of the following:
   • Click on any specific host to examine its vulnerabilities in the Hosts tab of the scan results.
   • To examine all vulnerabilities in the scan results, select the Vulnerabilities tab.
2. Enter words to filter for matches in vulnerability names in the Search Vulnerabilities box above the vulnerabilities table. Nessus selects the results for you as you write based on the text you enter.

Creating a Filter

1. Pick one of the following:
   • Select the Hosts tab from the scan results.
   • To examine a host's vulnerabilities, click on it under the Hosts page of the scan results.
   • To examine all vulnerabilities, select the Vulnerabilities tab in the scan results.
2. Next to the search box, select Filter. A Filter window will display.
3. Pick your filtering choices:
   • matching any or all: When you choose All, only the results that satisfy all filters are displayed. When you choose Any, all of the filters' matching results are displayed.
   • Plugin characteristic: The descriptions of the plugin attribute can be found in the table of plugin attributes.
   • Argument filter: To clarify how the filter should match the selected plugin attribute, select is equal to, is not equal to, contains, or does not contain.
   • Value: You can either enter a value or choose one from a drop-down menu depending on the plugin attribute you chose.
4. (Optional) A new filter can be added by clicking.
5. Select Apply

Your filters are applied by Nessus, and the table displays vulnerabilities that match them.