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fix: an app's certificate authenticates as the KMS to any guest that pins the root CA - #1255
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- Remove the doc comment left dangling on AppIdValidator after moving validate_kms_rpc_cert into cert-client. - Lowercase the server cert usage error message. - Shorten history-narrating comments. - Replace ra-tls tests that only asserted sign_csr copies its input with a single fail-closed test; condense the cert-client TLS tests.
The root pin plus the kms:rpc usage already identify the KMS. Verifying its quote on every SignCert added a collateral fetch per GetTlsKey and made that path depend on collateral availability. Also let the test server bind port 0 and report it on liftoff instead of racing a released port, and stop shadowing app_info in sign_csr.
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September 24, 2026 04:09
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#1255 made SignCert stamp the verified app info instead of the requester's claims. tc-kms-keys-certs-004 decodes the leaf and requires app:custom, a real device_id rather than sha256(""), and the authorized vm_config os_image_hash. Signed-off-by: Kevin Wang <wy721@qq.com>
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…tls test count #1333 makes --verify-cert report is_valid false with a reason when the attested app info does not decode; run its test from the verifier binary. The ra-tls suite grew (#1232, #1255), so match any passing count and keep requiring the named tests. Signed-off-by: Kevin Wang <wy721@qq.com>
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Problem
The KMS signs a per-app CA under the same root every guest pins, and
SignCertcopies an app's requested SANs andserverAuthusage into the leaf.cert-clientpinned that root with nocert_validator, so it checked only chain + hostname: any app authorized for key release could mint a certificate for the KMS hostname, and a network attacker holding it would be accepted as the KMS forSignCert/GetMeta. (GetAppKeyindstack-utilwas not affected — it already checks the usage.)Two related issues in the same path:
device_idwas alwayssha256("")in KMS-issued certificates:sign_csrdecoded app info from the requester's unverifiedAttestation<()>, which has no device id.os_image_hashin the certificate came from the config embedded in the CSR, not thevm_configthe KMS authorized. Nothing binds that embedded config to the quote on TDX, so a requester could make the two disagree.Fix
cert-clientinstallsvalidate_kms_rpc_cert(requiresspecial_usage == "kms:rpc"), now shared withdstack-utilinstead of duplicated. Apps can't choose this value: the KMS writeskms:rpconly on its own RPC cert andapp:customon everything it signs for apps. The KMS quote is not re-verified per call: the root pin pluskms:rpcalready identify the KMS.CaCert::sign_csrtakesapp_info: Option<&AppInfo>(the identity the signer verified) instead ofapp_id, and stamps both app extensions from it. It refuses a CSR asking forext_app_infowhen none is supplied.attestation.decode_app_info_ex(false, &request.vm_config)— the same verified attestation andvm_configit authorized. Runtime measurements are unchanged; for honest callers onlydevice_id(now real) andos_image_hashdiffer.Name constraints / SAN allowlists / EKU restrictions were deliberately not used: apps are meant to get
serverAuthcertificates for their own domains.Tests
cert-client: serves a real app leaf (root →derive_app_ca→sign_csr) and a realkms:rpcleaf over TLS, and drives the production client config against both: the app cert is refused, the KMS cert is accepted.ra-tls:sign_csrrefuses to embed app info the signer did not supply.cargo test -p cert-client -p ra-tls -p dstack-kmspasses;cargo check -p dstack-util -p dstack-guest-agent --all-targetsis clean.