We covered Sigma rules in Chapter 5, Working with Data, but just to refresh your memory, Sigma rules are the YARA rules of log files. Sigma allows the community to share detection rules using a specific "language" that can be translated into different SIEM formats.
Now, let's learn how to use Sigma rules for our detections.
One important thing to keep in mind while creating rules is that they shouldn't be so generic that they trigger without any malicious behaviour occurring. Rules have to be broad enough to capture procedure variations, but also not too broad that they start overloading the analyst with false positives.
Let's create a rule for our initial access file. Keep in mind that this rule will only be useful if we are completely sure that there are no screensavers in our environment that require internet connection, such as, for example, a screensaver connecting to a weather site.
The first thing we need to...