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CVE-2026-96770

s2s-proxy accepts untrusted client certificates

CVSS 4.0 9.3 CRITICALCheck source for fixed versionsKEV status unknown

Original advisory

Historical advisory recorded 23 Oct 2026 15:48:27 UTC. Read the latest advisory.

cve-program · CVE-2026-96770

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-96770

Published

github.com/temporalio/s2s-proxy

https://pkg.go.dev

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "Temporal Technologies, Inc.",
                    "product": "s2s-proxy",
                    "collectionURL": "https://pkg.go.dev",
                    "packageName": "github.com/temporalio/s2s-proxy",
                    "repo": "https://github.com/temporalio/s2s-proxy",
                    "programFiles": [
                        "encryption/tls.go"
                    ],
                    "programRoutines": [
                        {
                            "name": "GetServerTLSConfig"
                        }
                    ],
                    "versions": [
                        {
                            "status": "affected",
                            "version": "0.0.1-alpha",
                            "lessThanOrEqual": "0.2.2",
                            "versionType": "semver"
                        }
                    ],
                    "defaultStatus": "unaffected"
                }

Original source record · Cite this exact observation · Complete original publisher JSON