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AutopilotMonitor/docs/backend
Oliver Kieselbach d6895f2c7e feat(security): enforce cert tenant binding — reject cross-tenant certificates
The Intune roots the chain is pinned to are shared by every Intune tenant, so
a valid certificate only ever proved "issued by Intune to someone". Tenant
scoping rested on the device serial, which is printed on the chassis. A
Mismatch now returns 403.

Switched on against measured data, not a hunch: 35,684 requests across 32
tenants since the shadow telemetry landed, every one a Match, with the
Warning channel independently verified to be carrying other traffic so the
zero could not be a telemetry artefact.

Only Mismatch blocks, and the rule lives in one function so "what rejects a
request" has a single answer. ExtensionMissing, Unparseable and
RequestTenantNotAGuid mean "cannot tell" and are tolerated: the sample only
covers devices active in the window, so an older certificate or a
sovereign-cloud CA could still lack the extension, and rejecting on absence
would lock those devices out for something outside their control.
ExtensionMissing is the candidate for later tightening and has its own test
pinning the tolerance, so removing it must be a decision.

Evaluation fails open on its own exception — a defect on our side is not
evidence of a cross-tenant certificate. The 403 body does not echo which
tenant the certificate belongs to; that pair goes to the rejection log.

Device binding (stage 3) is untouched: still shadow, still Global-Admin-only.

Backend 4638/4638, 0 warnings.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-25 12:45:21 +02:00
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