Tag Archives: Nessus

Adding custom NASL plugins to Tenable Nessus

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Making custom NASL scripts (plugins) for Nessus is a pretty complicated process. Basically, NASL (Nessus Attack Scripting Language) is an internal instrument of Tenable and it seem that they are not really interested in sharing it with the community. The only publicly available official documentation, NASL Reference Guide and NASL2 reference manual, was written at least 13 years ago. Certainly many things changed since then in the actual product.

Adding custom NASL plugins to Tenable Nessus

However, it’s still possible to add custom NASL scripts into the plugin set of your Nessus server. Let’s see how to do it. Everything was tested in the latest Nessus 8.

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What’s new in Nessus 8

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Today Tenable released a new version of their famous vulnerability scanner – Nessus 8. The existing scanner nodes don’t see the updates yet, but the installation binaries are already available. So you may try to install it.

What's new in Tenable Nessus 8

This major release will be way more positive than the previous one. Of course Tenable did NOT return the multi-user mode and API in Nessus Professional. But on the other hand, they did NOT cut the functionality even further. They even added new features in GUI. And, what is the most important, they did NOT switch to the assets-based licensing (at least yet). 🙂

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Asset Inventory for Internal Network: problems with Active Scanning and advantages of Splunk

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In the previous post, I was writing about Asset Inventory and Vulnerability Scanning on the Network Perimeter. Now it’s time to write about the Internal Network.

Typical IT-infrastructure of a large organization

I see a typical IT-infrastructure of a large organization as monstrous favela, like Kowloon Walled City in Hong Kong. At the beginning it was probably wisely designed, but for years it  was highly effected by spontaneous development processes in various projects as well as multiple acquisitions. And now very few people in the organization really understand how it all works and who owns each peace.

There is a common belief that we can use Active Network Scanning for Asset Inventory in the organization. Currently, I’m not a big fan of this approach, and I will try to explain here the disadvantages of this method and mention some alternatives.

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Asset Inventory for Network Perimeter: from Declarations to Active Scanning

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In the previous post, I shared some of my thoughts about the good Asset Inventory system. Of course, for me as a Security Specialist, it would be great if IT will provide such magical system. 🙂 But such an ideal situation is rarely possible. So now let’s see how to build an Asset Inventory system using the resources of Information Security team.

There are no special secrets. It’s necessary to get information about the assets from all available IT systems and then get the rest of the data using our own Assessment tools. I would like to start with hosts on Network Perimeter. The Network Perimeter targets are available at any time for hacker attacks, that’s why this part of the network is the most critical.

Asset Inventory for Network Perimeter

Network Perimeter is like the Wall in the Game of Thrones. The same white walkers are hiding behind the wall and our task is to find the breaches in the wall faster than potential intruders. “Night gathers, and now my watch begins”. (c)

Perimeter is changing constantly. And we should understand at any time what hosts are currently exposed in every office and every external hosting platform.

We can get information about external hosts using some Vulnerability Scanner located on external host in the Internet. I have already wrote about it briefly in  Vulnerability Management for Network Perimeter. Here I would like focus on how we can understand which hosts should be scanned and what useful information we can get from the raw scan results.

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Free High-Tech Bridge ImmuniWeb Application Discovery service

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Today I would like to talk about another service for application security analysis by High-Tech Bridge. It’s called ImmuniWeb Application Discovery.

This service can get information about your web and mobile applications available from the Internet. Believe me, this is not so obvious for a large organization. And, what is especially pleasant, it works automatically and free of charge. 😉

High-Tech Bridge ImmuniWeb Free Application Discovery

ImmuniWeb Application Discovery will also show the basic security problems with SSL connection, web-server headers, potential phishing issues for all founded web services. You can read more about this part in my posts about High-Tech Bridge services and APIs for SSL/TLS server testing and for searching cybersquatting, typosquatting and phishing domains.

From the same interface you can order an advanced audit of your web applications by High-Tech Bridge as well.

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Vulnerability Databases: Classification and Registry

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What publicly available Vulnerability Databases do we have? Well, I can only say that there are a lot of them and they are pretty different. Here I make an attempt to classify them.

It’s quite an ungrateful task. No matter how hard you try, the final result will be rather inaccurate and incomplete. I am sure someone will be complaining. But this is how I see it. 😉 If you want to add or change something feel free to make a comment bellow or email me@avleonov.com.

The main classifier, which I came up with:

  • There are individual vulnerability databases in which one identifier means one vulnerability. They try to cover all existing vulnerabilities.
  • And others are security bulletins. They cover vulnerabilities in a particular product or products. And they usually based on on patches. One patch may cover multiple vulnerabilities.

I made this diagram with some Vulnerability Databases. Note that I wanted to stay focused, so there are no exploit DBs, CERTs, lists of vulnerabilities detected by some researchers (CISCO Talos, PT Research, etc.), Media and Bug Bounty sites.

Vulnerability Databases classification

For these databases the descriptions of vulnerabilities are publicly available on the site (in html interface or downloadable data feed), or exist in a form of paid Vulnerability Intelligence service (for example, Flexera).

On one side there are databases of individual vulnerabilities, the most important is National Vulnerability Database. There are also Chinese, Japanese bases that can be derived from NVD or not.

On the other side we have security bulletins, for example RedHat Security Advisories.

And in the middle we have a Vulnerability Databases, for which it is not critical whether they have duplicated vulnerability IDs or not.

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Potential RCE in Nessus 7 and attacks on Vulnerability Scanners

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A few days ago I saw an interesting youtube video (UPD. 14.05.18 Not available anymore). It is demonstrating the exploitation of the RCE vulnerability in Tenable Nessus Professional 7.0.3. Currently we have very few information about this vulnerability: only youtube video, which is mentioned only on ExploitWareLabs.

Nessus 7.0.3 RCE

While there is no exploit in public access, it’s hard to say how it actually works. It’s also not clear what versions of Nessus are affected. 7.0.3 is the latest version currently. Because of API disabling in Nessus 7 many users are still on 6.11.3. It is not clear whether they are affected or not.

This even can be a fake video. Therefore, I specifically write “potential RCE”. I will update this post when more data is available.

UPD. 14.05.18 In the comments to my post anonymous account Destring Portal posted a comment with the second video of Nessus RCE exploitation and it seems, that it was made by the same author. In this video, the author runs a remote shell on the Nessus host and executes various commands. I will add review of this second video bellow.

Nessus RCE second video

UPD. 10.05.18 Renaud Deraison, Co-Founder and CTO of Tenable, commented on my post at Linkedin:

Our research team studied the video and we have several reasons to doubt its authenticity. We’ve conducted a thorough audit over the last 48 hours based the few details that are in the video and didn’t find anything. We reached out the researcher and instead of replying he removed the video*. We’ll communicate if indeed there is a risk.

In general, you are right though – the security of scanners is of paramount importance. This actually is a topic I’ve been extremely worried about ever since the early days of Nessus. We have a number of security mechanisms in place (interpreted language for the detection scripts, ciphered temporary files, very limited runtime environment) which really aim to limit the risk of being exploited but also to mitigate the risk should the scanner be compromised. I actually did a few talks in the past about scanning “rogue hosts” and we continue to treat all input as hostile.

Again, we’re continuing to investigate the matter and will let you know if we find anything.

* currently video is still available on the same address; it could be probably blocked for some time. (UPD. 14.05.18 Not available anymore)

In any case, it’s a good reason to talk about vulnerabilities of such kind, how they appear and how to protect Vulnerability Scanners from attackers.

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