Tag Archives: Linux

Can a Vulnerability Scan break servers and services?

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Can a Vulnerability Scan break servers and services? The most serious problem of Vulnerability Scanners is that they are too complex and unpredictable. Usually they don’t affect the target hosts, but when they do, welcome to hell! And if you scan huge infrastructure, tens thousands hosts and more, it’s not “if” the scanner will break the server it’s “when” it will do it.

As a responsible person for Vulnerability Management you will be also responsible for all the troubles that VM product can make in the IT infrastructure. And what will you say to the angry mob of your colleagues from IT and Business when they will be quite curious to know why did the service/server go down after the scan? Actually, it’s not much to say.

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Vulnerability Management at Tinkoff Fintech School

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Vulnerability Management at Tinkoff Fintech School. In the last three weeks, I participated in Tinkoff Fintech School – educational program for university students. Together with my colleagues, we prepared a three-month practical Information Security course: 1 lecture per week with tests and home tasks.

Each lecture is given by a member of our security team, specialized in one of the following modules: Vulnerability Management, Application Security, Infrastructure Security, Network Security, Virtualization Security, Banking Systems Security, Blue & Red-teaming, etc.

Vulnerability Management at Tinkoff Fintech School

The course is still ongoing, but my Vulnerability Management module is over. Therefore, I want to share my impressions and some statistics.

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Martian Vulnerability Chronicles

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Martian Vulnerability Chronicles. Well, there should have been an optimistic post about my vulnerability analysis & classification pet-project. Something like “blah-blah-blah the situation is pretty bad, tons of vulnerabilities and it’s not clear which of them can be used by attackers. BUT there is a way how to make it better using trivial automation“. And so on. It seems that it won’t be any time soon. ¯\_(ツ)_/¯

I’ve spent several weekends on making some code that takes vulnerability description and other related formalized data to “separate the wheat from the chaff”. And what I get doesn’t look like some universal solution at all.

Pretty frustrating, but still an interesting experience and great protection from being charmed by trendy and shiny “predictive prioritization”.

Martian Vulnerability Chronicles

Literally, when you start analyzing this vulnerability-related stuff every your assumption becomes wrong:

  • that vulnerability description is good enough to get an idea how the vulnerability can be exploited (let’s discuss it in this post);
  • that CVSS characterizes the vulnerability somehow;
  • that the links to related objects (read: exploits) can be actually used for prioritization.

Actually, there is no reliable data that can be analyzed, trash is everywhere and everybody lies 😉

Let’s start from the vulnerability description. Great example is the last week critical Linux kernel vulnerability CVE-2019-8912.

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What’s new in Nessus 8

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What’s new in Nessus 8. 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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Assessing Linux Security Configurations with SCAP Workbench

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Assessing Linux Security Configurations with SCAP Workbench. Recently I had a chance to work with OpenSCAP. It’s a set of free and open-source tools for Linux Configuration Assessment and  a collection security content in SCAP (Security Content Automation Protocol) format.

In this post I will write about SCAP Workbench. It is a GUI application that can check the configuration of your local Linux host (or the remote host via ssh; note that agent installation is required), and show the settings that are not comply with some security standard, for example PCI DSS or DISA STIG.

SCAP Workbench PCI DSS CentOS7 localhost

Moreover, you can generate the script for automated remediation. You can also create your own scan profiles based on existing  SCAP content.

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Vulnerability Databases: Classification and Registry

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Vulnerability Databases: Classification and Registry. 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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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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