SigmaHQ Sigma Rules

What it is

Sigma is a generic, YAML-based signature format for describing detection logic against log data, similar in spirit to how Snort or YARA rules describe network or file patterns, but aimed at SIEM and log analysis. A Sigma rule describes a log source, a set of matching conditions and metadata such as severity and references, and can then be converted with separate open source converter tooling into the native query language of many different backends.

The SigmaHQ repository

The SigmaHQ GitHub repository is the main community collection of ready-written Sigma rules, covering detections across Windows event logs, Linux auditing, cloud provider logs, network devices and more. Even without writing a single rule of your own, reading through the repository is a genuinely useful way to learn what suspicious activity looks like in raw log form, since each rule documents the specific log fields and values it watches for.

How to use it

Start by reading a handful of existing rules for techniques you already recognise, for example a rule detecting a specific living-off-the-land binary being invoked with suspicious arguments, to see how the abstract description maps to concrete log fields. From there, convert a rule to your own SIEM's query language using the separate open source Sigma conversion tooling, and test it against your own log data in a lab or non-production environment before relying on it.

Who it is for

Security analysts and detection engineers who want detection logic that is not locked to one vendor's proprietary query language. It is equally useful as a learning resource for anyone trying to understand common attacker techniques described in concrete, log-level terms rather than abstract prose.

Free versus paid

The Sigma format and the SigmaHQ rule repository are entirely free and open source. Some commercial security platforms bundle curated or premium Sigma rule packs as part of a paid product, but the open community rules and the format itself carry no cost.

Prerequisites

Comfort reading YAML and at least a basic understanding of the log source you are working with, such as Windows event logs, helps a lot. Mapping techniques to a framework such as MITRE ATT&CK, which many Sigma rules already reference, is a useful parallel study.

Common questions

Do I need my own SIEM to benefit from this? No, reading existing rules teaches detection thinking even without a SIEM to run them in.

How current are the rules? The repository is actively maintained with frequent contributions; always check a rule's last update date and test it against your own data before trusting it in production.

Does Sigma replace vendor-specific detection content? No, it complements it; many teams use Sigma rules as a portable baseline and still write vendor-specific detections for platform-specific telemetry.