CVE-2026-105236: CWE-295 Improper Certificate Validation in Erlang OTP

The vulnerability arises from the ssl application's handling of TLS 1.2 session resumption when multiple SNI virtual hosts share a single listener socket. The server keeps one pre-TLS 1.3 session cache per listener and does not associate cached sessions with the specific SNI name or client trust policy that established them. When the server switches to verify_peer mode without disabling session reuse, the ssl_config:update_options/3 function inherits reuse_sessions=true from the base listener, allowing session reuse in client-authenticating servers. During abbreviated handshakes, the ssl_session:is_resumable/4 function only verifies that the cached session uses a current server certificate and includes some peer certificate, but it does not revalidate the peer certificate against the CA selected for the requested SNI name. This flaw enables a client authenticated to one SNI host to authenticate to another SNI host on the same listener if the hosts share a server certificate, such as wildcard or multi-SAN certificates. TLS 1.3 does not use this session cache and is unaffected. The affected versions include Erlang/OTP from 18.0 before 27.3.4.19 and ssl from 7.0 before 11.2.12.14, among others.

An attacker holding a client certificate trusted by one SNI virtual host can authenticate to a different SNI virtual host on the same listener by resuming a TLS 1.2 session. This improper certificate validation could lead to unauthorized authentication across SNI hosts sharing the same server certificate. TLS 1.3 is not impacted, limiting the scope to TLS 1.2 sessions. There are no known exploits in the wild at this time.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since no explicit patch links or official fixes are provided in the input data, users should monitor Erlang/OTP vendor advisories for updates addressing this issue. Until a fix is applied, consider disabling TLS 1.2 session reuse on servers serving multiple SNI virtual hosts with client authentication to mitigate the risk.