Legacy SIEM coverage gaps: are your logs actually complete?

TL;DR: Legacy SIEMs often appear healthy while silently dropping critical telemetry, leaving investigations without authentication, firewall, or workload evidence when incidents begin, according to DataBahn. The real problem is governance of data coverage, not just log volume, because blind spots and low-value ingestion both undermine detection and response.

NHIMG editorial — based on content published by DataBahn: Why are Legacy SIEMs a problem?

Questions worth separating out

Q: What breaks when critical log sources silently stop sending data?

A: When critical sources go silent, the SIEM may still look healthy while investigations lose the evidence needed to reconstruct authentication activity, privilege changes, and attack timelines.

Q: Why do AI coding tools increase governance risk for IAM and NHI teams?

A: AI coding tools increase governance risk because they obscure who created the logic, which identities executed it, and whether the resulting automation has the right access scope.

Q: How do you know if telemetry coverage is actually working?

A: Coverage is working when every critical source has an owner, an expected event profile, and a monitored last-seen state.

Practitioner guidance

• Validate source-by-source coverage Build a live inventory of every critical log source with owner, criticality, expected frequency, and last-seen status so silent sources are visible within minutes, not weeks.
• Monitor for silent, whispering, and noisy sources Classify telemetry streams by health so teams can detect sources that stopped, degraded, or spiked abnormally before incidents expose the gap.
• Tie each source to accountable ownership Map every feed to a business unit or application owner in the CMDB so coverage failures trigger the right remediation path instead of a generic operations ticket.

What's in the full article

DataBahn's full article covers the operational detail this post intentionally leaves for the source:

• Automatic source inventory fields including source type, volume, frequency, format, owner, and compliance classification.
• Health-state logic for classifying streams as healthy, silent, whispering, or noisy.
• End-to-end lineage tracking from collection through parsing, enrichment, transformation, and destination.
• CMDB-enriched source context for linking telemetry to business unit and asset criticality.

👉 Read DataBahn's analysis of legacy SIEM coverage gaps and telemetry visibility →

Legacy SIEM coverage gaps: are your logs actually complete?

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