All published s2s-proxy versions through 0.2.2 are affected. In versions 0.1.16 through 0.2.2, TLS server listeners use Go's RequireAnyClientCert mode when skipCAVerification is false. This mode checks that the client holds the certificate's private key but does not verify the certificate against the configured CA. An attacker can therefore use a self-signed certificate and key to establish a TLS and yamux connection, then invoke RPCs allowed by the proxy's configuration and Temporal credentials. No certificate or private key trusted by the deployment, and no Temporal credential, is required.

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Advisories

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Fixes

Solution

The fix is expected in version 0.2.3. Upgrade to version 0.2.3 or later when available.


Workaround

Restrict the listener to known peer addresses or a private network, or use a TLS terminator that verifies client certificates against the intended CA. These controls reduce exposure but do not fix the proxy defect.

History

Wed, 23 Sep 2026 20:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Wed, 23 Sep 2026 19:15:00 +0000

Type Values Removed Values Added
Description All published s2s-proxy versions through 0.2.2 are affected. In versions 0.1.16 through 0.2.2, TLS server listeners use Go's RequireAnyClientCert mode when skipCAVerification is false. This mode checks that the client holds the certificate's private key but does not verify the certificate against the configured CA. An attacker can therefore use a self-signed certificate and key to establish a TLS and yamux connection, then invoke RPCs allowed by the proxy's configuration and Temporal credentials. No certificate or private key trusted by the deployment, and no Temporal credential, is required.
Title s2s-proxy accepts untrusted client certificates
Weaknesses CWE-296
References
Metrics cvssV4_0

{'score': 9.3, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:H/SI:H/SA:H'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: Temporal

Published:

Updated: 2026-09-23T19:36:12.488Z

Reserved: 2026-09-23T16:06:36.077Z

Link: CVE-2026-96770

cve-icon Vulnrichment

Updated: 2026-09-23T19:36:10.230Z

cve-icon NVD

Status : Received

Published: 2026-09-23T19:19:55.013

Modified: 2026-09-23T20:17:27.193

Link: CVE-2026-96770

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

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Weaknesses