The weak point is the bridge between Nitro Enclaves and KMS, not KMS itself. Even with correct attestation and cryptography, the surrounding SDK and integration code can still break enclave trust or steer key handling the wrong way.
Trail of Bits says it is cataloging attack classes against the enclave-KMS channel and disclosing vulnerabilities in the Nitro Enclaves SDK for C. The report centers on AWS Nitro Enclaves, AWS KMS, and the C SDK, and it shows that policy checks and attestation only hold if the client side asks for keys safely and correctly.
For teams using attestation-backed cloud secrets, the security boundary includes the glue code as much as the cloud service. That makes the integration layer a real attack surface, even when the underlying crypto primitives are sound.