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02/08/2026 11:41 am
TL;DR: SIEM detections often underperform because source data is missing, malformed, or filtered before it reaches the analytics layer, leaving rules unable to fire even when they look complete on paper, according to DataBahn. The governance problem is telemetry assurance: if you cannot prove the right events, fields, and schemas are flowing, you do not have reliable detection coverage.
NHIMG editorial — based on content published by DataBahn: Why are Legacy SIEMs a problem? That's the gap most organizations don't see until it's too late
Questions worth separating out
Q: What breaks when SIEM telemetry is incomplete?
A: Detection rules break first, then trust in the SIEM follows.
Q: Why do identity events matter so much in SIEM and SOAR design?
A: Identity events often show compromise earlier than infrastructure telemetry because attackers usually start by abusing accounts, tokens, or authentication paths.
Q: How do security teams know if SIEM coverage is actually working?
A: They verify the path from source to rule, not just the rule itself.
Practitioner guidance
- Validate event codes before rule deployment Confirm that every detection dependency has a corresponding source event, such as failed logons, Kerberos events, or process creation records, before the rule moves into production.
- Build source-to-rule coverage maps Document which telemetry source, event type, and field set supports each high-value detection so blind spots are visible when log forwarding changes or filtering rules are introduced.
- Normalise logs into a common schema Standardise incoming telemetry into a consistent schema such as OCSF, CIM, or ECS so analytics do not break when source formats differ across vendors or platforms.
What's in the full article
DataBahn's full article covers the operational detail this post intentionally leaves for the source:
- Event-code validation examples that show how to prove a rule has the telemetry it needs before production filtering changes.
- Schema normalisation examples across common log formats, including how field consistency supports reliable correlation.
- MITRE ATT&CK coverage mapping details that connect telemetry gaps to specific techniques and log source requirements.
- Volume-reduction safeguards that preserve detection dependencies while lowering SIEM ingestion cost.
👉 Read DataBahn's analysis of why SIEM detections fail when telemetry is incomplete →
SIEM telemetry gaps: what IAM and SOC teams need to verify?
Explore further
02/08/2026 12:53 pm
Telemetry assurance is now a governance control, not a logging concern. If teams cannot prove that the right event types, codes, and fields are arriving, detection coverage is theoretical. The operational mistake is treating ingestion as a plumbing issue instead of a control boundary. For identity programmes, that means authentication and privilege events need explicit collection assurance, not just SIEM onboarding.
A question worth separating out:
Q: Who is accountable when cost-cutting removes detection telemetry?
A: Accountability sits with the control owners who approve filtering changes, because volume reduction can become a security decision rather than a storage decision. Governance should require proof that the altered pipeline still supports required detections and response use cases before any reduction is made.
👉 Read our full editorial: SIEM coverage fails when telemetry is incomplete, not when rules are weak
