During our research about UEBA tools, we noticed that these tools are gaining ground on SIEM solutions, with some organizations opting to focus their monitoring efforts on UEBA instead of SIEM. That brings the question, why?
The fact is, as much as we like to talk about it, Events correlation on SIEM was overrated. SIEM correlation has always been weak, too simplistic. Most cases are basic boolean chaining of events, “if this AND this AND that OR that happens, alert”. There are not many cases where this type of correlation can be written in a way that it’s not checking for a very specific attack path, one from the many thousand possibilities. In other words it is hard to generalize the use cases, so the organization needs to keep producing these rules to specific cases, with the risk of drowning in false positives if it tries to make things more productive. In the end, SIEM use cases are mostly smarter filtering and aggregation.
Yes, there are more modern rules options available. You can build rules that will have dynamic thresholds and do some smarter anomaly detection, but it is still very simplistic when compared to the generalized models from UEBA tools. They have less use cases but with a broader coverage for threats. If properly implemented, they are more effective.
Another key difference between UEBA tools and SIEM is that SIEM correlation is usually built to generate alerts for each use case. Potential threats are still looked in isolation. Some SIEMs will aggregate things based on IP and time (think the “offenses” concept from Qradar, for example), but the goal is aggregation and alert reduction, not correlation. UEBAs, on the other hand, keep risk scores (I hate the term; there’s no “risk” there, but whatever) for entities such as endpoints and users, with the use cases adding to the scores of the involved entities. The nice thing about scores is that they provide the ability to correlate things that may initially look unrelated. Different use cases involving a certain entity will raise the score to a level that makes the entity interesting and subject to investigation, without the need for an analyst to envision the possibility of those events being part of a single occurrence and implementing that as a correlation rule.
SIEM correlation is still useful, but we need to recognize its limitations and embrace the new capabilities of new tools such as UEBA to improve that. As we’ve been talking, SIEM and UEBA are getting closer every day, so now it’s just a matter of time before SIEMs move (or give the option) to track issues based on entity scores. But if you want to have that now, you should look at UEBA tools.