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[REVIEW] detection-engineering: add data-source health and telemetry drift evidence gates #1578

@wangedmund77-cmyk

Description

@wangedmund77-cmyk

Skill Being Reviewed

Skill name: detection-engineering
Skill path: skills/secops/detection-engineering/SKILL.md

False Positive Analysis

Benign code/configuration that can be over-flagged:

rule: impossible_travel
data_source: okta_signin
health: last_event_age_minutes < 10, parser_version pinned, sample count monitored

Why this is a false positive:
rule: impossible_travel can be safe when the missing compensating evidence is present, but the current skill does not ask reviewers to distinguish that evidence from the risky pattern. The review should require proof of the guardrail before escalating severity.

Coverage Gaps

Missed variant 1:

rule enabled: true
source: endpoint_process_events
# EDR connector last successful ingestion was 9 days ago

Why it should be caught:
This variant leaves a realistic attack path open while still satisfying the current high-level checklist language.

Missed variant 2:

sigma_rule maps field CommandLine
SIEM parser renamed field to process.command_line, rule silently matches zero events

Why it should be caught:
This is a common production edge case where policy exists on paper but does not bind the runtime behavior or evidence trail.

Edge Cases

A detection rule can be syntactically correct and mapped to ATT&CK while producing no alerts because telemetry is stale, parser mappings drifted, or expected event volume collapsed.

Remediation Quality

  • Fix resolves the vulnerability
  • Fix doesn't introduce new security issues
  • Fix doesn't break functionality
  • Issues found: Add gates for data source freshness, parser/schema version, expected event volume, zero-match anomaly, last successful ingestion, and replay test using known-good events.

Comparison to Other Tools

Tool Catches this? Notes
Sigma tooling Partial Validates rule syntax, not source health.
SIEM content packs Partial Assume mappings are current.
Detection-as-code tests Partial Good when they include replay/field mapping fixtures.

Overall Assessment

Strengths:
The skill is strong on ATT&CK mapping and rule design.

Needs improvement:
It should require telemetry health evidence before rating a detection as effective.

Priority recommendations:

  1. Add a data-source health precondition to every detection review.
  2. Require replay tests or recent match evidence for critical detections.
  3. Flag schema/parser drift and zero-match periods as coverage failures, not just operational notes.

Bounty Info

  • I have read and agree to the CONTRIBUTING.md bounty terms
  • Preferred payment method: Crypto or PayPal after maintainer acceptance.

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