CoCoS attested TLS is vulnerable to relay attacks via extracted ephemeral TLS keys

Summary

CVE	CVE-2026-33697
State	PUBLISHED
Assigner	GitHub_M
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-03-27 00:16:23 UTC
Updated	2026-03-30 13:26:29 UTC
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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N

EPSS: 0.000040000 probability, percentile 0.001430000 (date 2026-04-01)

Problem Types: CWE-322 | CWE-346 | CWE-322 CWE-322: Key Exchange without Entity Authentication | CWE-346 CWE-346: Origin Validation Error

Version	Source	Type	Score	Severity	Vector
3.1	[email protected]	Secondary	7.5	HIGH	`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N`
3.1	CNA	DECLARED	7.5	HIGH	`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N`

CVSS v3.1 Breakdown

Attack Vector

Local

Attack Complexity

High

Privileges Required

Low

User Interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

None

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Ultravioletrs	Cocos	affected >= 0.4.0, < 0.8.2	Not specified

References

Reference	Source	Link	Tags
github.com/ultravioletrs/cocos/security/advisories/GHSA-vfgg-mvxx-mgg7	[email protected]	github.com
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

No vendor comments have been submitted for this CVE.

There are currently no legacy QID mappings associated with this CVE.