Zerologon and the Role of Monitoring in Vulnerability Management

Published on October 8, 2020

By Augusto Barros, Vice President of Solutions


Vulnerability management is one of the most basic security hygiene practices organizations must have in place to avoid being hacked. However, even being a primary security control doesn't make it simple to successfully implement. I used to cover VM in my Gartner days, and it was sad to see how many organizations were not doing it properly.

Many security professionals see VM as a boring topic, usually seeing it simply as a "scan and patch" cycle. Although the bulk of a typical VM program may indeed be based on the processes of scanning for vulnerabilities and applying patches, there are many other things that need to be done so it can deliver the expected results.

One of the most important pieces of it is the prioritization of findings. It is clear to most organizations that patching every open vulnerability is just not feasible. If you can't patch everything, what should you patch first? There are many interesting advancements in this area. What used to be based only on the severity of the vulnerabilities (the old CVSS value) is now a more sophisticated process that leverages multiple data points, including threat intelligence. The EPSS research by Kenna Security is a great example of how evolved the practice of prioritizing vulnerabilities is now when compared to the old CVSS times.

But even when you are able to decide what to patch first, there are also cases where the remediation is not simply applying a patch. Some vulnerabilities involve not only a bug, but also other issues such as the existence of legacy software and protocols in the environment. These situations usually require a more complex approach, and that's where an additional component of the VM process, the compensating controls, become important.

Compensating controls are used to address the risk of a vulnerability while the full remediation cannot be applied. Using an IPS, for example, is a typical compensating control. You can use them when you cannot apply the remediation, such as when a patch is not available, or to mitigate the risk until you are comfortable enough (usually after testing is done, during a maintenance window) to apply it. We usually see some security controls that can avoid or reduce the impact of vulnerability exploitation as the ideal candidates for compensating risk, but there is something I always like to bring up during this discussion: Monitoring.

Think about it for a second. You have an open vulnerability that you still cannot patch. The exploit is available, as well as a lot of information about how it is used. Even if you cannot avoid it, you can use all this information to build a security monitoring use case focused on the exploitation of this specific vulnerability. You it is there, and that there is a chance for it being exploited, so why not put something together to look for that exploitation? You can prioritize the alerts generated by this use case, as you know you are currently vulnerable to that type of attack.

A great example of using security monitoring as part of the VM process is what is happening with the new Windows Zerologon EP (ZEP) vulnerability (CVE-2020-1472). The issue is complex and requires more than just applying a patch. Our VP of Threat Research, Oleg Kolesnikov, produced a great write-up about the details and also variants of exploitation and detection. In summary, Microsoft has provided a patch for the immediate problem, but some third-party systems may still use an older, vulnerable version of Netlogon secure channel connections. To avoid breaking functionality of existing systems, Microsoft has introduced new events in their logs to identify the use of these older versions, and signaled they will move to an enforcement mode that will not accept them anymore after February, 2021.

This is where aligning monitoring with the remediation process becomes so important. The new events added by Microsoft can help identify attack attempts and track other vulnerable systems on the network.  A pre-established process to coordinate the use of monitoring tools and infrastructure as an additional compensating control for VM can help in situations like this, where the plan to handle a vulnerability also requires monitoring activities.