# CVE-2026-96770: s2s-proxy accepts untrusted client certificates

> CVE-2026-96770: s2s-proxy accepts untrusted client certificates. CVSS 9.3 (CVSS 4.0).

Canonical: https://rewindex.com/cve/CVE-2026-96770
Last updated: 2026-09-24T20:43:32Z

- Published: 2026-09-23 18:58 UTC · Updated: 2026-09-24 20:43 UTC · Assigner: Temporal
- CVSS: 9.3 (CVSS 4.0) · Severity: Critical
- EPSS: 0.32%, 25th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-296

## 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.

## Affected vendors and products

- Temporal Technologies, Inc.: s2s-proxy

## Tracked companies

- [Temporal Cloud](https://rewindex.com/company/temporal-cloud.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-96770)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-96770)
- [https://docs.temporal.io/production-deployment/data-encryption\#codec-server-setup](https://docs.temporal.io/production-deployment/data-encryption#codec-server-setup)
- [https://github.com/temporalio/s2s-proxy/blob/v0.2.2/encryption/tls.go\#L47-L62](https://github.com/temporalio/s2s-proxy/blob/v0.2.2/encryption/tls.go#L47-L62)
- [https://github.com/temporalio/s2s-proxy/commit/d100c2258dbc37d7df51298ea045315f36c7eb3b](https://github.com/temporalio/s2s-proxy/commit/d100c2258dbc37d7df51298ea045315f36c7eb3b)
- [https://github.com/temporalio/s2s-proxy/commit/f1dc6b9a3919d37e82545ab461cbe6bb62618d3c](https://github.com/temporalio/s2s-proxy/commit/f1dc6b9a3919d37e82545ab461cbe6bb62618d3c)
- [https://github.com/temporalio/s2s-proxy/pull/296](https://github.com/temporalio/s2s-proxy/pull/296)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-96770 · Markdown: https://rewindex.com/cve/CVE-2026-96770.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-96770 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:12:12.769Z