Non-reliable Nessus scan results

Do you perform massive unauthenticated vulnerability scans with Nessus? It might be a bad idea. It seems that Nessus is not reliable enough to assess hundreds and thousands of hosts in one scan and can lose some valuable information.

Non-reliable Nessus scan results

The thing is that sometimes Nessus does not detect open ports and services correctly. And without successful service detection it will not launch other vulnerability detection plugins (see Nessus Scan stages in my post about Tenable University ). Scan results for the host will be empty, however in reality it may have some critical vulnerabilities, that you simply will not see!

Upd. When you use Nessus inside your corporate network only, it might not be issue for you. But if you deploy Nessus on some remote hosting to perform regular perimeter scans, emulating attacker’s actions, it’s quite a possibility that you will face such kind of errors. Especially if Nessus and scan targets are placed in different geograpfical locations and it takes many hops for Nessus to reach each target. If you use load balancers in your organisation to increase capacity and reliability of applications, this can also lead to errors.

Anyway, it’s good to know when Nessus was not able to detect services on some hosts and you should not relly on these  scan results. Let’s see how we can figure this out.

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Masking Vulnerability Scan reports

Continuing the series of posts about Kenna (“Analyzing Vulnerability Scan data“, “Connectors and REST API“) and similar services. Is it actually safe to send your vulnerability data to some external cloud service for analysis? Leakage of such information can potentially cause great damage to your organization, right?

Masking Vulnerability Scans

It’s once again a problem of trust to vendor. IMHO, in some cases it may make sense to hide the real hostnames and ip-addresses of the target hosts in scan reports. So, it would be clear for analysis vendor that some critical vulnerability exists somewhere, but it would not be clear where exactly.

To do this, each hostname/ip-address should be replaced to some values of similar type and should be replaced on the same value each time. So the algorithms of Kenna-like service could work with this masked reports. This mean that we need to create a replacement dictionary.

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Tenable University: Nessus Certificate of Proficiency

Yesterday I finished “Nessus Certificate of Proficiency” learning plan at Tenable University and passed the final test. Here I would like to share my impressions.

Nessus Certificate test completed

First of all, few words about my motivation. I use Nessus literally every day at work. So, it was fun to check my knowledge. I already wrote about Tenable education portal in “Study Vulnerability Assessment in Tenable University for free” post. It’s free. It’s available for everyone on demand. However, Tenable customers get access to way more content.

At this moment there are four learning plan available for Tenable customers: for Nessus,, SecurityCenter and SecurityCenter Continuous View. Each learning plan consist of short video lessons grouped in courses and the final test.

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Kenna Security: Connectors and REST API

In the last post about Kenna Security cloud service I mentioned their main features for analyzing data from different vulnerability scanners. Now let’s see how to import Tenable Nessus scan results in Kenna. Here you can see the list of connectors for all supported products:

Kenna connectors

Three connectors for Nessus are available:

  • Nessus Importer retrieves existing scan results from your Nessus server.
  • Nessus Scanner can schedule scans on your Nessus server.
  • Nessus XML imports xml (.Nessus2) files.

First two connectors work with Nessus server directly. And they probably won’t work anymore with Nessus Professional 7, because of API removing (see “New Nessus 7 Professional and the end of cost-effective Vulnerability Management (as we knew it)“). If Nessus server is deployed on-premise you should use special Kenna Virtual Tunnel.

Last “Nessus XML” connector is the most flexible. No matter how you got your scan results, it will be possible to import them to Kenna. See how to get XML reports from from Nessus server in a post “Retrieving scan results through Nessus API“.  You can upload XML scan results using Kenna web GUI (not very efficient way, but for testing – why not?) or REST API.

To use Kenna REST API you will need an Application Token. Go to the the Settings menu -> Applications:

Kenna settings

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Nessus Manager disappeared and On-Prem was announced

If you open Tenable Products page right now you will not see Nessus Manager there anymore.  Nessus Manager page “The Power of Nessus for Teams” was also deleted.

Tenable products

However, it is still mentioned in the product comparison. Agent-Based Scanning in SecurityCenter and SecurityCenter Continuous View “* Requires Vulnerability Management or Nessus Manager for agent management.”

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