trusted execution environments. In versions up to and including 0.8.2, the intra-handshake attested TLS (aTLS) Intel TDX verification path does not copy the expected current-session freshness value into the TDX quote-body policy before quote validation, so structurally valid TDX QuoteV4 Evidence is accepted without checking that its REPORTDATA field matches the reportData expected for the current session. A relying party using this path can therefore accept Evidence with a mismatched or reused reportData and release application data after the handshake, enabling session-misbinding to an unintended attestation context. The issue is fixed in version 0.9.0.

Cocos AI is a confidential computing system for running AI workloads inside trusted execution environments. In versions up to and including 0.8.2, the intra-handshake attested TLS (aTLS) AMD SEV-SNP verification path does not enforce attestation freshness when the expected reportData value is nil, empty, or omitted, leaving the SEV-SNP policy ReportData unset so the verifier accepts unrelated or stale Evidence not bound to the current connection. A relying party that uses this path without an expected reportData as a trust or authorization decision can be induced to trust an unintended attestation context; a supplied non-empty reportData is still validated. The issue is fixed in version 0.9.0.

Cocos AI is a confidential computing system for AI. The current implementation of attested TLS (aTLS) in CoCoS is vulnerable to a relay attack affecting all versions from v0.4.0 through v0.8.2. This vulnerability is present in both the AMD SEV-SNP and Intel TDX deployment targets supported by CoCoS. In the affected design, an attacker may be able to extract the ephemeral TLS private key used during the intra-handshake attestation. Because the attestation evidence is bound to the ephemeral key but not to the TLS channel, possession of that key is sufficient to relay or divert the attested TLS session. A client will accept the connection under false assumptions about the endpoint it is communicating with — the attestation report cannot distinguish the genuine attested service from the attacker's relay. This undermines the intended authentication guarantees of attested TLS. A successful attack may allow an attacker to impersonate an attested CoCoS service and access data or operations that the client intended to send only to the genuine attested endpoint. Exploitation requires the attacker to first extract the ephemeral TLS private key, which is possible through physical access to the server hardware, transient execution attacks, or side-channel attacks. Note that the aTLS implementation was fully redesigned in v0.7.0, but the redesign does not address this vulnerability. The relay attack weakness is architectural and affects all releases in the v0.4.0–v0.8.2 range. This vulnerability class was formally analyzed and demonstrated across multiple attested TLS implementations, including CoCoS, by researchers whose findings were disclosed to the IETF TLS Working Group. Formal verification was conducted using ProVerif. As of time of publication, there is no patch available. No complete workaround is available. The following hardening measures reduce but do not eliminate the risk: Keep TEE firmware and microcode up to date to reduce the key-extraction surface; define strict attestation policies that validate all available report fields, including firmware versions, TCB levels, and platform configuration registers; and/or enable mutual aTLS with CA-signed certificates where deployment architecture permits.