Vulnerability · Published Sep 23, 2026 · Assigned by Temporal
CVE-2026-96770s2s-proxy accepts untrusted client certificates
Critical 9.3
In plain English
A critical-severity security flaw in s2s-proxy from Temporal Technologies, Inc.. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities).
Official 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 products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Temporal Technologies, Inc. | s2s-proxy | 0.0.1-alpha – through 0.2.2 |
Weakness: CWE-296 · 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