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Protocol security review — 0.6.2

This focused maintainer review covers CtapCbor.cs and WebAuthnService.cs. It is not a third-party independent audit.

Confirmed findings fixed

  • User verification was preferred, not required: both Windows ceremonies used value 2. They now use WEBAUTHN_USER_VERIFICATION_REQUIREMENT_REQUIRED (1) and reject authenticator data without both UP and UV.
  • Health checks did not verify assertion signatures: registration now stores the canonical ES256 COSE public key. Health checks verify the signature over authenticatorData || SHA256(clientDataJSON).
  • Returned WebAuthn context was trusted without binding checks: registration and assertion now verify the fixed RP-ID hash, credential ID, flags, credential type, signature presence, native lengths/pointers, and unsolicited data.
  • Signature counters were accepted without clone/malfunction detection: a non-zero counter must increase relative to the encrypted vault record.
  • AAGUID byte order was interpreted as a native GUID: AAGUID is now formatted using network byte order.
  • CTAP CBOR accepted non-canonical encodings: the decoder rejects non-minimal integers/lengths, unsorted keys, indefinite lengths, unsupported composite keys, invalid UTF-8, and duplicate byte-string keys.
  • CTAP object allocation was bounded only per collection: encoding and decoding now enforce document, collection, depth, and total-value ceilings.
  • CBOR map encoding depended on dictionary insertion order: map keys are sorted using CTAP2 canonical major-type, encoded-length, and bytewise ordering.
  • Temporary native requests were freed without clearing: tracked unmanaged strings, buffers, and structures are cleared before release.

Regression coverage

The suite covers canonical ordering, non-minimal encodings, duplicate structural keys, composite keys, excessive nesting/collections/object counts, deterministic malformed-input fuzzing, RP mismatch, missing UV, credential mismatch, signature tampering, and counter rollback. The full hardware/security suite passes 20/20 on an Infineon TPM 2.0.

Residual risk

  • The Windows WebAuthn API and authenticator firmware remain trusted dependencies.
  • Registration requests none attestation, so the application validates possession and protocol binding rather than asserting manufacturer provenance.
  • Existing Windows Hello or external credentials lack the newly stored public key and must be re-registered for cryptographic health verification.
  • A third-party source audit and production trusted code-signing certificate are still required before calling the project production-ready.