Sigma Rules: Vendor-Agnostic Detection in 2026

Last updated: April 26, 2026

Sigma is to detection rules what YAML is to configuration — a vendor-neutral format that compiles to specific SIEM query languages. Splunk SPL, Elastic EQL, Microsoft Sentinel KQL, Chronicle, Sumo Logic, Wazuh — all consume Sigma rules via converters. This article covers writing Sigma, the public rule repositories worth using, and the pragmatic deployment workflow for a multi-vendor SIEM environment.

The motivation

Detection rules used to be vendor-locked. A Splunk rule wouldn’t run on Sentinel without rewriting. As organisations adopt multiple SIEM tools — primary SIEM + cloud-native logs + EDR-bundled SIEM — rule duplication explodes. Sigma solves this by separating logical detection from query syntax.

Sigma rule structure

title: PowerShell Encoded Command Execution
id: 5d6a1b6e-...
status: experimental
description: Detects PowerShell execution with encoded command (-enc / -EncodedCommand)
references:
  - https://attack.mitre.org/techniques/T1059/001/
author: Author Name
date: 2026/04/26
tags:
  - attack.execution
  - attack.t1059.001
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    Image|endswith: '\powershell.exe'
    CommandLine|contains:
      - ' -enc '
      - ' -EncodedCommand '
      - ' -e '
  filter:
    User: 'NT AUTHORITY\SYSTEM'
  condition: selection and not filter
falsepositives:
  - Legitimate admin scripts that use encoded commands
level: medium

Key fields: logsource identifies the data source; detection contains selection/filter logic; condition combines them.

Public rule repositories

• SigmaHQ/sigma — official MITRE-aligned community rules. ~3000 rules covering most ATT&CK techniques.
• Florian Roth’s rules (Neo23x0) — high-quality, often the source for SigmaHQ.
• Joe Security / mthcht / others — vendor-specific Sigma collections (cloud, AWS, M365).
• Velociraptor artifact library — Sigma compatible for endpoint hunting.

Start with SigmaHQ; add specific vendor packs as needed.

Conversion workflow

# Install pySigma + backend
pip install pysigma pysigma-backend-splunk pysigma-backend-elasticsearch

# Convert single rule to Splunk SPL
sigma convert -t splunk rule.yml

# Convert directory recursively
sigma convert -t splunk -O cluster_blocks rules/ > splunk-rules.txt

# For Elastic EQL:
sigma convert -t elasticsearch rule.yml

Output is the SIEM-native query that you import into your platform.

Deployment pattern

1. Curate. Don’t import every public rule — false-positive volume kills SOC capacity. Pick rules relevant to your environment and ATT&CK priorities.
2. Tune in audit mode. Deploy as alerting-disabled / informational level for 30 days. Observe false-positive rate.
3. Tune logic. Adjust selection/filter to your environment’s known-good patterns.
4. Promote to alerting. Set severity, response runbook, on-call rotation.
5. Validate. Run Atomic Red Team simulation; confirm rule fires on the technique.
6. Maintain. Quarterly review: rules with no fires in 90 days — does the technique no longer apply, or is the rule broken?

Authoring custom rules

For environment-specific detections (your organisation’s app names, internal IP ranges, custom processes):

• Start from a similar SigmaHQ rule.
• Adjust logsource to your data source.
• Customise selection for your environment’s specifics.
• Add filter blocks for known-good patterns.
• Test conversion to your SIEM and validate via simulation.
• Contribute back to community where the rule is generic.

Compliance angle

• SEBI CSCRF — detection-rule library expectation. Sigma is the de-facto vendor-neutral format.
• NIST 800-53 IR-4 — detection capability evidence.
• ISO 27001:2022 A.8.16 — monitoring activities.

The takeaway

Sigma turns detection-engineering from a vendor-specific scripting exercise into a portable, version-controlled, peer-reviewable practice. Every modern SOC should have a Sigma rule library in version control, tied to the ATT&CK matrix, with simulation evidence per rule. The investment in this discipline compounds — as your SIEM stack changes, your detection logic doesn’t have to.