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My Sigma rule was silently failing and the test suite didn't catch it

DEV Community·Jude Hilgendorf·28 days ago
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I'm 18, taking cybersecurity at a community college in Michigan, and most of my detection engineering knowledge comes from reading other people's Sigma rules at like 1am. So when I started building SIEMForge, an open source toolkit that bundles Sigma rules with a Sysmon config and Wazuh custom rules mapped to MITRE ATT&CK, I figured the rules part would be the easy bit. Wrong. Here's the bug that took me two evenings to actually understand. The setup SIEMForge ships with 10 detections in rules/sigma/ . They cover the usual suspects: PowerShell download cradles, LSASS dumps, mshta and rundll32 abuse, Run key persistence, scheduled tasks, that kind of thing. There's also a CLI scanner I wrote that loads every rule and runs it against a log file (JSON, JSONL, syslog, or CSV). The point is to test rules locally before you ship them into Splunk or Elastic, so you don't write a rule, deploy it, and then realize three weeks later that it's never fired.…

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