fix(verify): fail closed on software-only and misbound external receipts#366
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Two fail-closed fixes in cmcp_verify.verify: 1. Software-only claims are no longer reported as VERIFIED. Previously a self-consistent software-only claim (no hardware-backed attestation) ended with failure=None and the status decision returned VERIFIED, contradicting LIMITATIONS.md, which states such claims are partially_verified. The status decision now forces PARTIALLY_VERIFIED whenever hardware_attestation is unverified and there is otherwise no failure. A real failure still takes precedence and is not downgraded. 2. External-execution-evidence misbinding now short-circuits. When external_evidence_keys is supplied and a receipt's linked_call_id does not match the entry call_id, verification recorded the mismatch but fell through and still ran the signature check, so a receipt bound to a different call could be reported signature-valid. A `continue` now stops processing that entry after the binding mismatch. Tests: software-only claim returns PARTIALLY_VERIFIED (not VERIFIED); hardware-backed happy path still returns VERIFIED; a real failure keeps its failure status; a linked_call_id mismatch is rejected and the receipt is not also reported signature-valid. Updated the CLI verify tests, which used a software-only fixture and previously asserted a full pass. Tracked Wave 2 follow-ups (not addressed here, require hardware-validated work): binding the audit-chain root into the attested report; making the cnf.jwk<->report_data binding fatal for SEV-SNP/TDX and fixing the TDX report_data offset; verifying the attestation report signatures (VCEK/DCAP/EK). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Summary
Two fail-closed fixes in
cmcp_verify.verify, both insrc/cmcp_verify/verify.py.1. Software-only claims must not report VERIFIED. A self-consistent software-only claim (no hardware-backed attestation) previously ended with
failure=None, and the status decision returnedVERIFIED. This contradictsLIMITATIONS.md, which states software-only claims arepartially_verified. The status decision now forcesPARTIALLY_VERIFIEDwheneverhardware_attestationis in the unverified set and there is otherwise no failure. A genuine failure still takes precedence and is not downgraded to partial.2. External-execution-evidence misbinding now short-circuits. When
external_evidence_keysis supplied and a receipt'slinked_call_iddoes not match the entrycall_id, the code recorded the mismatch but fell through and still verified the receipt signature, so a receipt bound to a different call could be reported signature-valid. Acontinuenow stops processing that entry after the binding mismatch.Tests
test_verify.py: software-only claim returnsPARTIALLY_VERIFIED(tightened, no longer acceptsVERIFIED); hardware-backed happy path returnsVERIFIED; a real failure keeps its failure status (not silently downgraded).test_audit_conformance.py: strengthened thelinked_call_idmismatch test to assert the misbound receipt is not also reported signature-valid.test_verify_command.py: updated three CLI tests that used a software-only fixture and previously asserted a full pass; they now assertRESULT: FAIL (partially_verified)and a non-zero exit, matchingLIMITATIONS.md.Validation:
pytest tests/unit(758 passed, 3 skipped) andtests/conformance(58 passed) green;ruff check src/ --select E,F,W --ignore E501clean.Tracked Wave 2 follow-ups (not in this PR)
These require hardware-validated work and are intentionally out of scope:
cnf.jwk<->report_databinding fatal for SEV-SNP/TDX, and fix the TDXreport_dataoffset.🤖 Generated with Claude Code