This is the first article in a series explaining the different types of penetration testing — or “pen tests” for short. Because while many…
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What is a Penetration Test?

Lars Greiwe

This is the first article in a series explaining the different types of penetration testing — or “pen tests” for short. Because while many people might know they need a pen test, the term “pen test” can actually mean different things, depending on what you’re testing, and from what perspective. This series will give an overview of each of the different types of penetration tests, with a view to helping IT and security teams decide which type of penetration testing they might benefit the most from.

So what is a penetration test?

Conducting a pen test involves tasking a security professional (or team of professionals) with taking an attacker’s perspective to try find the security holes in your systems before the hackers do. They will use the same techniques that a real attacker would use, whilst being careful to carry out tests in a manner which avoids causing any damage to your live systems. The idea is to discover the vulnerabilities in your systems and inform you of any security holes which can subsequently be shored up. All types of penetration testing culminate in the delivery of a formal report, with advice on how to fix all of the issues that were found.

As we’ve said above, there are many different flavours of penetration test, some of which include:

But without further ado, let’s introduce the first type of pen test in the series:

Perimeter Penetration Testing

Otherwise known as an “External Pen Test”, the perimeter test involves taking a more conventional “Hacker’s-Eye View”. This type of test is carried out in a way which would emulate a hacker sitting on their computer, somewhere on the internet. The aim is to find ways to compromise your systems or steal your data by finding vulnerabilities in your systems, software and services which are exposed to the open internet, your “Internet-facing” systems.

Typically these types of test will involve scanning for and (where possible) safely exploiting “Known Vulnerabilities” in software and hardware. ‘Known vulnerabilities’ is a phrase used to describe programming flaws in software which are already known to the security community, as they have either been publicly disclosed by a security researcher or a product vendor. Information on how to exploit these known vulnerabilities is often freely available to hackers and security professionals, and so having known vulnerabilities present in your systems is a serious threat.

Perimeter penetration testing will identify these flaws using a number of methods. This can include grabbing banners that your systems are broadcasting containing software version numbers, and attempting exploits to test if you are vulnerable.

If you haven’t conducted any kind of penetration testing before, a perimeter or ‘external’ test is often the best place to start, as the perimeter is the easiest thing for attackers to get to, and attackers always take the path of least resistance. So if you have trivial vulnerabilities in your perimeter, that’s where they’ll get you.

If you’re interested in what vulnerabilities you might have in your perimeter, make sure you check out Intruder’s free trial, to see whether you have any known weaknesses in your perimeter systems today. Be warned though, the vulnerabilities you have today might be different from the ones you have tomorrow, as around 8,000 new ones get discovered each year (about 20 a day)!

There are services are out there to help deal with this problem, such as our Intruder Pro and Baseline services, that provide continuous, rolling perimeter penetration testing and vulnerability scanning. Our services provide a level of coverage unparalleled by scheduled yearly or quarterly scanning, since we are watching our customers’ internet facing systems all the time. For more info, don’t hesitate to get in touch.

Next up in the series, we’ll discuss the other types of penetration test you might want to conduct after your perimeter test, so make sure to check back soon.

Release Date
Level of Ideal
Before CVE details are published
Limited public information is available about the vulnerability.

Red teamers, security researchers, detection engineers, threat actors have to actively research type of vulnerability, location in vulnerable software and build an associated exploit.

Tenable release checks for 47.43% of the CVEs they cover in this window, and Greenbone release 32.96%.
Day of CVE publish
Vulnerability information is publicly accessible.

Red teamers, security researchers, detection engineers and threat actors now have access to some of the information they were previously having to hunt themselves, speeding up potential exploit creation.

Tenable release checks for 17.12% of the CVEs they cover in this window, and Greenbone release 17.69%.
First week since CVE publish
Vulnerability information has been publicly available for up to 1 week.

The likelihood that exploitation in the wild is going to be happening is steadily increasing.

Tenable release checks for 10.9% of the CVEs they cover in this window, and Greenbone release 20.69%.
Between 1 week and 1 month since CVE publish
Vulnerability information has been publicly available for up to 1 month, and some very clever people have had time to craft an exploit.

We’re starting to lose some of the benefit of rapid, automated vulnerability detection.

Tenable release checks for 9.58% of the CVEs they cover in this window, and Greenbone release 12.43%.
After 1 month since CVE publish
Information has been publicly available for more than 31 days.

Any detection released a month after the details are publicly available is decreasing in value for me.

Tenable release checks for 14.97% of the CVEs they cover over a month after the CVE details have been published, and Greenbone release 16.23%.

With this information in mind, I wanted to check what is the delay for both Tenable and Greenbone to release a detection for their scanners. The following section will focus on vulnerabilities which:

These are the ones where an attacker can point their exploit code at your vulnerable system and gain unauthorised access.

We’ve seen previously that Tenable have remote checks for 643 critical vulnerabilities, and OpenVAS have remote checks for 450 critical vulnerabilities. Tenable release remote checks for critical vulnerabilities within 1 month of the details being made public 58.4% of the time, but Greenbone release their checks within 1 month 76.8% of the time. So, even though OpenVAS has fewer checks for those critical vulnerabilities, you are more likely to get them within 1 month of the details being made public. Let’s break that down further.

In Figure 10 we can see the absolute number of remote checks released on a given day after a CVE for a critical vulnerability has been published. What you can immediately see is that both Tenable and OpenVAS release the majority of their checks on or before the CVE details are made public; Tenable have released checks for 247 CVEs, and OpenVAS have released checks for 144 CVEs. Then since 2010 Tenable have remote released checks for 147 critical CVEs and OpenVAS 79 critical CVEs on the same day as the vulnerability details were published. The number of vulnerabilities then drops off across the first week and drops further after 1 week, as we would hope for in an efficient time-to-release scenario.

Figure 10: Absolute numbers of critical CVEs with a remote check release date from the date a CVE is published

While raw numbers are good, Tenable have a larger number of checks available so it could be unfair to go on raw numbers alone. It’s potentially more important to understand the likelihood that OpenVAS or Tenable will release a check of a vulnerability on any given day after a CVE for a critical vulnerability is released. In Figure 11 we can see that Tenable release 61% their checks on or before the date that a CVE is published, and OpenVAS release a shade under 50% of their checks on or before the day that a CVE is published.

Figure 11: Percentage chance of delay for critical vulnerabilities

So, since 2010 Tenable has more frequently released their checks before or on the same day as the CVE details have been published for critical vulnerabilities. While Tenable is leading at this point, Greenbone’s community feed still gets a considerable percentage of their checks out on or before day 0.

I thought I’d go another step further and try and see if I could identify any trend in each organisations release delay, are they getting better year-on-year or are their releases getting later? In Figure 12 I’ve taken the mean delay for critical vulnerabilities per year and plotted them. The mean as a metric is particularly influenced by outliers in a data set, so I expected some wackiness and limited the mean to only checks released 180 days prior to a CVE being published and 31 days after a CVE being published. These seem to me like reasonable limits, as anything greater than 6 months prior to CVE details being released is potentially a quirk of the check details and anything after a 1-month delay is less important for us.

What can we take away from Figure 12?

Figure 12: Release delay year-on-year (lower is better)

With the larger number of checks, and still being able to release a greater percentage of their remote checks for critical vulnerabilities Tenable could win this category. However, the delay time from 2019 and 2020 going to OpenVAS, and the trend lines being so close, I am going to declare this one a tie. It’s a tie.

The takeaway from this is that both vendors are getting their checks out the majority of the time either before the CVE details are published or on the day the details are published. This is overwhelmingly positive for both scanning solutions. Over time both also appear to be releasing remote checks for critical vulnerabilities more quickly.

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Written by

Lars Greiwe

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