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Introducing Nuclei: the scanner that packs a punch

Daniel Andrew
Author
Daniel Andrew
Head of Security Services

Key Points

Like antivirus software, vulnerability scans rely on a database of known weaknesses and are only as good as the latest update.

Even if you choose a solution using the best industry-leading scanners, there could be weaknesses that they might miss. Which is why we've augmented Intruder with another scanner – and we’re really excited to tell you about it. We’ve always believed in being the best, and adding Nuclei is the next step to providing the best vulnerability management platform on the market.

What is Nuclei?

Nuclei is an open-source vulnerability scanning engine which is fast, extensible, and covers a wide range of weaknesses. It’s become increasingly popular with bug bounty hunters, penetration testers and researchers who want to produce repeatable checks for serious weaknesses.

These experts, working with the Nuclei’s own team at ProjectDiscovery, combine their knowledge and insights about cutting-edge weaknesses to produce checks extremely fast – which makes scanning as soon as possible after a vulnerability is discovered.  

What does Nuclei add to Intruder?

Intruder is adding Nuclei as a scanning engine to augment and enhance our attack surface checks for customers, such as login panels that shouldn’t be internet exposed, and a wider range of checks for known vulnerabilities in services which are typically internet-exposed.

Nuclei augments Intruder’s existing scanning engines by helping you discover more about your attack surface – because you can’t protect what you don’t know about – by providing even more coverage than the powerful scanning engines we already use under the hood, such as Tenable and OpenVAS.

With over 3,000 additional checks in the initial release, Intruder will offer much broader and deeper coverage and discovery capabilities that can’t be matched by using a single vulnerability scanner alone.

Check out our metrics on how Nuclei and Tenable complement each other.

The benefits of using multiple scanning engines  

Generally speaking, vulnerability scanners aim to produce checks for as many vulnerabilities as possible. However, the number of vulnerabilities discovered year on year is now so high (more than 25,000 already this year), that it’s impossible for a single scanning engine to keep up with them all. As a result, even the very best, industry-leading leading scanners will struggle to check for every known vulnerability out there.

In fact, our analysis from early 2023 which compared Tenable’s Nessus (an industry leading scanner we use at Intruder) and OpenVAS (an open-source scanner) showed significant differences in coverage between scanners:

“Tenable checks for 12,015 CVEs which OpenVAS does not check for and OpenVAS checks for 6,749 CVEs which Tenable does not check for.”

And even though your chosen scanner may be making sensible decisions on which vulnerabilities to write checks for (like whether it has been seen exploited in the wild, or whether it’s in software products which are very widely used) some may get missed.  

Unfortunately, this could include software that your organization uses – and it’s a harsh reality that one day you may find out that you’ve been compromised via an attack vector which your scanner(s) simply don’t yet have a check for.

So, the simple answer is to have multiple scanning engines. Provided their capabilities don’t significantly overlap (which is inefficient and duplicates work), having several complementary scanners improves coverage by finding more vulnerabilities, discovering more about what your attack surface looks like.

How will this reduce your attack surface?

Nuclei brings specific detection and discovery capabilities which are an integral part of attack surface reduction (ASR). By adding this capability to detect more systems and panels that are exposed, you’ll get the knowledge you need to help you decide which of those really need to be exposed, and which can be hardened.  

The size of your attack surface, and how well it’s managed, is closely tied to your risk of opportunistic attackers exploiting your systems. The less you expose, and the more hardened the services you expose are, the harder it is for an attacker to exploit a weakness.

Want to know more?

Interested in learning more about Nuclei and Intruder? Talk to us.

 

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Introducing Nuclei: the scanner that packs a punch

Daniel Andrew

Like antivirus software, vulnerability scans rely on a database of known weaknesses and are only as good as the latest update.

Even if you choose a solution using the best industry-leading scanners, there could be weaknesses that they might miss. Which is why we've augmented Intruder with another scanner – and we’re really excited to tell you about it. We’ve always believed in being the best, and adding Nuclei is the next step to providing the best vulnerability management platform on the market.

What is Nuclei?

Nuclei is an open-source vulnerability scanning engine which is fast, extensible, and covers a wide range of weaknesses. It’s become increasingly popular with bug bounty hunters, penetration testers and researchers who want to produce repeatable checks for serious weaknesses.

These experts, working with the Nuclei’s own team at ProjectDiscovery, combine their knowledge and insights about cutting-edge weaknesses to produce checks extremely fast – which makes scanning as soon as possible after a vulnerability is discovered.  

What does Nuclei add to Intruder?

Intruder is adding Nuclei as a scanning engine to augment and enhance our attack surface checks for customers, such as login panels that shouldn’t be internet exposed, and a wider range of checks for known vulnerabilities in services which are typically internet-exposed.

Nuclei augments Intruder’s existing scanning engines by helping you discover more about your attack surface – because you can’t protect what you don’t know about – by providing even more coverage than the powerful scanning engines we already use under the hood, such as Tenable and OpenVAS.

With over 3,000 additional checks in the initial release, Intruder will offer much broader and deeper coverage and discovery capabilities that can’t be matched by using a single vulnerability scanner alone.

Check out our metrics on how Nuclei and Tenable complement each other.

The benefits of using multiple scanning engines  

Generally speaking, vulnerability scanners aim to produce checks for as many vulnerabilities as possible. However, the number of vulnerabilities discovered year on year is now so high (more than 25,000 already this year), that it’s impossible for a single scanning engine to keep up with them all. As a result, even the very best, industry-leading leading scanners will struggle to check for every known vulnerability out there.

In fact, our analysis from early 2023 which compared Tenable’s Nessus (an industry leading scanner we use at Intruder) and OpenVAS (an open-source scanner) showed significant differences in coverage between scanners:

“Tenable checks for 12,015 CVEs which OpenVAS does not check for and OpenVAS checks for 6,749 CVEs which Tenable does not check for.”

And even though your chosen scanner may be making sensible decisions on which vulnerabilities to write checks for (like whether it has been seen exploited in the wild, or whether it’s in software products which are very widely used) some may get missed.  

Unfortunately, this could include software that your organization uses – and it’s a harsh reality that one day you may find out that you’ve been compromised via an attack vector which your scanner(s) simply don’t yet have a check for.

So, the simple answer is to have multiple scanning engines. Provided their capabilities don’t significantly overlap (which is inefficient and duplicates work), having several complementary scanners improves coverage by finding more vulnerabilities, discovering more about what your attack surface looks like.

How will this reduce your attack surface?

Nuclei brings specific detection and discovery capabilities which are an integral part of attack surface reduction (ASR). By adding this capability to detect more systems and panels that are exposed, you’ll get the knowledge you need to help you decide which of those really need to be exposed, and which can be hardened.  

The size of your attack surface, and how well it’s managed, is closely tied to your risk of opportunistic attackers exploiting your systems. The less you expose, and the more hardened the services you expose are, the harder it is for an attacker to exploit a weakness.

Want to know more?

Interested in learning more about Nuclei and Intruder? Talk to us.

 

Release Date
Level of Ideal
Comments
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:

  • Have CVSSv2 rating of 10
  • Are exploitable over the network
  • Require no user interaction

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?

  • We can see that between 2011 and 2014 Greenbone’s release delay was better than that of Tenable, by between 5 and 10 days.
  • In 2015 things reverse and for 3 years Tenable is considerably ahead of Greenbone by a matter of weeks.
  • But, then in 2019 things get much closer and Greenbone seem to be releasing on average about a day earlier than Tenable.
  • For both the trendline over an 11-year period is very close, with Tenable marginally beating Greenbone.
  • We have yet to have any data for 2021 for OpenVAS checks for critical show-stopper CVEs.
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.

Written by

Daniel Andrew

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