CVE-2026-96770 s2s-proxy accepts untrusted client certificates
Attackers can bypass TLS client certificate verification to establish connections and invoke RPCs without valid credentials.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-96770?
CVE-2026-96770 is a critical authentication bypass vulnerability in Temporal Technologies, Inc. s2s-proxy, published on 23 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-296
Which versions are affected by CVE-2026-96770?
How do I fix CVE-2026-96770?
No fix has been published for CVE-2026-96770 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-96770 being exploited?
There is no known exploitation of CVE-2026-96770 in the wild and no public exploit code.
Sources
Also known as GHSA-fhc4-rg5x-86fx.