Tag Archives: Nessus

Potential RCE in Nessus 7 and attacks on Vulnerability Scanners

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Potential RCE in Nessus 7 and attacks on Vulnerability Scanners. 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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CISO Forum and the problems of Vulnerability Databases

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CISO Forum and the problems of Vulnerability Databases. Last Tuesday, April 24,  I was at “CISO FORUM 2020: glance to the future“. I presented there my report “Vulnerability Databases: sifting thousands tons of verbal ore”. In this post, I’ll briefly talk about this report and about the event itself.

CISO Forum 2020

My speech was the last in the program. At the same time, in a parallel stream, there was another interesting presentation by the most famous Russian information security blogger. Thus, there was a real danger of speaking in an empty room. 🙂 But everything went well. There were about 30 spectators and we had an active QA session afterwards.

As I wrote earlier, I started preparing my CyberCentral presentation several months before the event. I did not want to tell the same story again at CISO Forum and PHDays. So I prepared 2 different presentations. At CyberCentral, I was talking about Vulnerability Scanners. And at CISO Forum I was talking mainly about Vulnerable Databases. Of course, I reused some materials, but the accents were different.

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My short review of “IDC Worldwide Security and Vulnerability Management Market Shares 2016”

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My short review of “IDC Worldwide Security and Vulnerability Management Market Shares 2016”. On February 12 IDC published new report about Security and Vulnerability Management market. You can buy it on the official website for $4500. Or you can simply download free extract on Qualys website (Thanks, Qualys!). I’ve read it and now I want to share my impressions.

IDC Worldwide Security and Vulnerability Management Market Shares 2016

I think it’s better start reading this report from the end, from “MARKET DEFINITION” section. First of all, IDC believe that there is a “Security and Vulnerability Management” (SVM) market. It consists of two separate “symbiotic markets”: security management and vulnerability assessment (VA).

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Dealing with Nessus logs

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Dealing with Nessus logs. Debugging Nessus scans is a very interesting topic. And it is not very well described even in Tenable University course. It become especially interesting when you see strange network errors in the scan results. Let’s see how we can troubleshoot Nessus scans without sending Nessus DB files to Tenable  (which is, of course, the default way 😉 ).

Nessus Logs

Default logging

Let’s see default Nessus logs. I cleared log nessusd.messages file to have only logs of the latest scan:

# echo "" > /opt/nessus/var/nessus/logs/nessusd.messages

and restarted Nessus:

# /bin/systemctl start nessusd.service

I scan only one host (test-linux-host01, 192.168.56.12) with the Advanced scan profile. No default settings was set.

As you can see from the cpe report, it’s typical Linux host with ssh server:

typical Linux host with ssh

What’s in the logs?

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Non-reliable Nessus scan results

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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

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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

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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, Tenable.io, SecurityCenter and SecurityCenter Continuous View. Each learning plan consist of short video lessons grouped in courses and the final test.

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