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Vulnerability States and the Over-Reliance on Numbers from Tools

I've just had a discussion with a fellow Head of Cybersecurity around vulnerabilities and two things struck me that people need to understand: firstly, vulnerabilities have different states and secondly, scanning tools don't have all the context so can't actually tell you what risk you are running. 

Our discussion started with a statement from them that vulnerabilities are black and white - they're either there or not. It's actually a bit more nuanced than that though. Without making this more complicated than it needs to be, inherently there are two states a vulnerability can be in: exploitable or unexploitable (sometimes called active or dormant with other subtleties). This doesn't mean that they are being exploited, but that it is either possible to exploit the vulnerability in the current configuration (however hard that may be) or it isn't without some other change happening first. 

In our discussion, my peer argued that if it is unexploitable then there is no vulnerability. I disagree with this point of view though. We are potentially only one configuration change or software upgrade from converting the unexploitable vulnerability into an exploitable one. We would be best off remediating this vulnerability if possible, but at a low priority level. Even if we choose not to remediate it now, we should still track it so that it doesn't come back to bite us unexpectedly in the future. 

The second part of the discussion was more important though. I stated that a critical vulnerability might actually be a fairly low risk in some circumstances, but a medium vulnerability might be an out of tolerance high risk in others. The response from my peer was surprising. They maintained that a critical was a critical and would be the top priority because the tooling had a scoring system. 

I tried to explain that I might have a system that stores confidential data, but that the availability of that data may not be time critical, for example I might be able to live with several hours downtime on an end of day reconciliation service - as long as I can reconcile before the markets open again my impact shouldn't be too high. If, on the other hand, all the positions became public knowledge or the integrity was tampered with, it would have a big impact. 

Now consider two different vulnerabilities: one critical vulnerability that only affects availability and a high that affects confidentiality and integrity. As long as I can recover within a matter of hours from an availability attack, this risk is likely to be lower than that associated with the high rated vulnerability, because the impact could be significantly higher. 

The vulnerability rating is a static score for the general case, which doesn't take into account your context. This aspect only really affects the likelihood part of the risk calculation. Different vulnerabilities expose you to different threat scenarios though, which may alter the impact. There are scoring mechanisms that take some of this into account, e.g. using the full CVSS calculation including the environmental and temporal modifiers as well, but this still doesn't give you the full context. 

Let me give you another example. Say that you have a vulnerability on your system that allows for a really easy privilege escalation - this is bad. But what if that vulnerability required a logged in user to perform the attack? Well, this could still be an issue on your workstation estate as users could escalate their privilege and attack the system. What if it's on a server protected by a privilege access management solution and no other users can log in? Now, the only people logging in already have elevated privileges and we can restrict their access to approved sessions only and record them into the bargain. Suddenly this isn't quite so much of a problem. 

Why don't the scanning tools that tell me I have a vulnerability know this? Well, how can they? Where are they going to get that context? It is possible in many cases to get more context, but only if you have multiple scanning technologies and cross-correlate all the findings, or get a security/risk professional. 

The key point I'm trying to make is that you can't just believe the numbers coming out of a tool that doesn't have all the context. This leads to focusing on what the tool thinks is the easiest vulnerability to exploit rather than the vulnerability carrying the highest risk. 

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