Description
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.
Published: 2026-03-26
Score: 7.5 High
EPSS: < 1% Very Low
KEV: No
Impact: Impersonation of an attested CoCoS service through a relay attack exploiting extracted transient TLS keys
Action: Apply hardening
AI Analysis

Impact

The vulnerability in CoCoS’s attested TLS allows a threat actor to extract the transient private key used in the TLS handshake. Possession of this key lets the attacker relay or redirect the TLS session, causing a client to believe it is communicating with the intended attested service when it is in fact a malicious relay. This breaks the authentication guarantees of attested TLS, enabling the adversary to impersonate the service, access confidential data, or execute unauthorized operations. The weakness is architectural and is unrelated to a specific software bug, relying on the design of the attestation process.

Affected Systems

The issue affects the CoCoS AI confidential computing system provided by ultravioletrs for all releases from version 0.4.0 through 0.8.2, including deployments on both AMD SEV‑SNP and Intel TDX platforms. No patch is currently available for this range of versions.

Risk and Exploitability

The CVSS score of 7.5 indicates a high severity, while the EPSS score is not published. The vulnerability is not listed in the CISA KEV catalog. Exploitability requires the attacker to first obtain the transient TLS private key, which can be achieved through physical access to the server hardware, transient execution attacks, or side‑channel attacks. Given the architectural nature of the flaw and the lack of a public patch, the risk is significant for any system that relies on CoCoS attested TLS for secure client‑server communication.

Generated by OpenCVE AI on March 27, 2026 at 06:27 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Ensure that the TEE firmware and processor microcode are current to reduce the key‑extraction surface
  • Implement strict attestation policies that validate all fields in the attestation report, including firmware versions, TCB levels, and platform configuration registers
  • If the deployment architecture permits, enable mutual attested TLS using CA‑signed certificates to bind the TLS channel to explicit certs

Generated by OpenCVE AI on March 27, 2026 at 06:27 UTC.

Tracking

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Advisories

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History

Fri, 27 Mar 2026 08:45:00 +0000

Type Values Removed Values Added
First Time appeared Ultravioletrs
Ultravioletrs cocos
Vendors & Products Ultravioletrs
Ultravioletrs cocos

Fri, 27 Mar 2026 04:00:00 +0000

Type Values Removed Values Added
Description 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.
Title CoCoS attested TLS is vulnerable to relay attacks via extracted ephemeral TLS keys
Weaknesses CWE-322
CWE-346
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N'}

Subscriptions

Ultravioletrs Cocos
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-03-26T23:34:53.414Z

Reserved: 2026-03-23T17:06:05.745Z

Link: CVE-2026-33697

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-03-27T00:16:23.133

Modified: 2026-03-27T00:16:23.133

Link: CVE-2026-33697

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-03-27T09:22:46Z

Weaknesses