s2s-proxy accepts untrusted client certificates
Summary
| CVE | CVE-2026-96770 |
|---|---|
| State | PUBLISHED |
| Assigner | Temporal |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-09-23 19:19:55 UTC |
| Updated | 2026-09-23 20:17:27 UTC |
| 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. |
Risk And Classification
Primary CVSS: v4.0 9.3 CRITICAL from [email protected]
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Problem Types: CWE-296 | CWE-296 CWE-296: Improper Following of a Certificate's Chain of Trust
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | [email protected] | Secondary | 9.3 | CRITICAL | 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/E:X/C... |
| 4.0 | CNA | CVSS | 9.3 | CRITICAL | 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 |
CVSS v4.0 Breakdown
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Temporal Technologies Inc. | S2s-proxy | affected 0.0.1-alpha 0.2.2 semver | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| docs.temporal.io/production-deployment/data-encryption | [email protected] | docs.temporal.io | |
| github.com/temporalio/s2s-proxy/commit/f1dc6b9a3919d37e82545ab461cbe6bb6... | [email protected] | github.com | |
| github.com/temporalio/s2s-proxy/commit/d100c2258dbc37d7df51298ea045315f3... | [email protected] | github.com | |
| github.com/temporalio/s2s-proxy/blob/v0.2.2/encryption/tls.go | [email protected] | github.com | |
| github.com/temporalio/s2s-proxy/pull/296 | [email protected] | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Praetorian, who reported this issue responsibly to Temporal Technologies (en)
Additional Advisory Data
Solutions
CNA: The fix is expected in version 0.2.3. Upgrade to version 0.2.3 or later when available.
Workarounds
CNA: 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.