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Nessus offline registration is a multi-step "sneakernet" process designed for air-gapped systems that cannot reach the internet to fetch updates. To register, you must bridge the gap between your offline scanner and Tenable’s online portal using a "challenge code" unique to your installation. The Registration Process

The "long story" involves jumping between two machines: your Offline Scanner and an Online Computer. Generate the Challenge Code (Offline System): Log into the machine where Nessus is installed.

Open a command prompt and run the command: nessuscli fetch --challenge.

Note the Code: You will receive a long alphanumeric string (e.g., aaaaaa11b2222cc33d44...) and a URL. Generate the License (Online Computer): Navigate to the Tenable Offline Registration page.

Enter your Challenge Code and your Activation Code (the license key you received via email).

Download Files: After submitting, the site will provide two critical items: The nessus.license file.

A link to download the Plugin Archive (a large compressed file like all-2.0.tar.gz). Complete the Activation (Offline System):

Transfer both the license and the plugin archive to the offline system via USB or secure media.

Register the License: Run nessuscli fetch --register-offline nessus.license.

Update Plugins: Use the command nessuscli update to load the vulnerability signatures. Key Hardware & Software Requirements

According to Tenable documentation, even in offline mode, ensure your system meets these specs: Install Tenable Nessus Offline

Prerequisites

  1. Nessus installed on the offline machine (Windows/Linux/macOS).
  2. A valid license (activation code from Tenable).
  3. A secondary machine with internet access to fetch the challenge file and download the license.

Troubleshooting

| Issue | Solution | |-------|----------| | Challenge code invalid | Regenerate challenge on the exact offline machine (changes after Nessus reinstall). | | License file not accepted | Ensure license matches the product (Pro vs Expert) and version (8.x vs 10.x). | | Web UI shows "unlicensed" | Check that nessusd is running and port 8834 is open. |

Important Notes

  • Offline plugin updates require downloading nessus-updates-<version>.tar.gz from Tenable and using: 
    nessuscli update /path/to/nessus-updates-<version>.tar.gz
  • Nessus Home (free) does not officially support offline activation. Use a Professional trial or purchased license.
  • For air-gapped networks, consider Tenable.sc (Security Center) which is designed for offline/static updates.

Step 2: Register Offline via Tenable

On a computer that has internet access:

  1. Go to the Tenable Offline Registration page:
    • Standard: https://plugins.nessus.org/v2/offline.php
    • US Government/Federal: https://plugins.nessus.org/v2/offline.php?federal=1 (Only use this if you have a Federal license).
  2. On this page, enter:
    • Your License Code.
    • The Challenge Code you generated in Step 1.
  3. Click Submit.
  4. The website will generate two things for you to download:
    • nessus-fetch.db (This contains your registration info).
    • All Plugins File (Usually a .gz or .zip file, this is very large, often 200MB+).

Note: Download the plugins file. Trying to update plugins offline without this file is very difficult.

2. Prerequisites for Offline Registration

| Requirement | Details | |-------------|---------| | Nessus version | 8.x, 9.x, 10.x (the process is similar) | | Activation code | Nessus Professional, Nessus Expert, or Tenable.io (some tiers support offline) | | Offline host | Linux, Windows, or macOS without internet | | Online machine | Any OS with browser & internet | | USB / secure transfer | To move files between machines |

Note: Nessus Essentials (free) generally does not support offline registration – it requires periodic online validation.