Use AAGUID to look up authenticator metadata in FIDO MDS3 and enforce authenticator policy
domain: fidoalliance.org · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
During attestation processing, extract the aaguid (16 bytes) from authenticatorData at byte offset 37; decode from packed CBOR if using packed attestation format.
Fetch the FIDO Metadata Service 3 (MDS3) JWT blob from https://mds3.fidoalliance.org/ — this is a signed JWT containing a list of authenticator metadata entries; verify the JWT signature against the MDS3 root certificate.
Look up the aaguid in the metadata entries; the entry contains description, authenticatorVersion, metadataStatement, and statusReports including certification status and known compromised statuses.
Apply your authenticator policy: reject credentials from authenticators with statusReports indicating USER_VERIFICATION_BYPASS, ATTESTATION_KEY_COMPROMISE, or other negative statuses; optionally allowlist only FIDO_CERTIFIED or higher.
Cache the MDS3 blob with the TTL indicated in the JWT (typically 24 hours) and refresh periodically; do not hardcode metadata.
Known gotchas
An aaguid of all zeros (00000000-0000-0000-0000-000000000000) indicates a self-attestation or 'none' attestation — the authenticator model is unknown and MDS3 lookup will find no entry.
Platform authenticators from Apple and Google may not be in MDS3 or may be listed under a batch aaguid; absence from MDS3 does not mean the authenticator is invalid — it means attestation cannot be verified against MDS3.
MDS3 status can change between credential registration and subsequent authentications; you may need to re-validate stored aaguids against updated MDS3 status on a schedule.
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