Detection Engineering

Sigma detection rules for my purple team homelab, validated on every commit with GitHub Actions.

What is this?

A collection of detection rules written in Sigma — a vendor-agnostic format that compiles down to whatever your SIEM speaks (Splunk SPL, Elastic KQL, Microsoft Sentinel, etc.). Each rule maps to a MITRE ATT&CK technique and is tested against my homelab's Splunk instance.

The CI pipeline validates syntax and converts every rule to Splunk SPL on push. If a rule is malformed or won't compile, the pipeline fails before it can reach the SIEM.

Rules

Rule	ATT&CK	Level
Brute Force - Multiple Failed Logons	T1110.001	High
Suspicious Encoded PowerShell	T1059.001	High
Office Application Spawning Interpreter	T1566.001 / T1204.002	High
LSASS Memory Access (Credential Dumping)	T1003.001	Critical
New Service Installed	T1543.003	Medium
Local User Account Created	T1136.001	Medium

Repo layout

├── .github/workflows/
│   └── validate.yml          # CI — lint + Splunk conversion
├── rules/
│   └── windows/
│       ├── authentication/   # Logon events
│       ├── process_creation/ # Sysmon process + access events
│       └── persistence/      # Services, accounts
└── README.md

CI Pipeline

Every push to main (or PR against it) triggers:

1. Syntax validation — sigma check ensures rules conform to the Sigma schema
2. Splunk conversion — sigma convert -t splunk compiles rules to SPL, catching field mapping issues

Writing a new rule

Rules follow the Sigma specification. Drop a .yml file in the appropriate rules/ subdirectory and push. The pipeline handles the rest.

Related

• range-as-code — the lab environment these detections run against
• homelab — architecture overview