Erlang OTP prior 27.3.4.18/28.5.0.7/29.1.1 SSL tls_client_connection_1_3:handle_server_hello improper authentication

Summaryinfo

A vulnerability marked as critical has been reported in Erlang OTP. Impacted is the function tls_client_connection_1_3:handle_server_hello of the component SSL. This manipulation causes improper authentication. This vulnerability is handled as CVE-2026-89422. The attack can be initiated remotely. There is not any exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in Erlang OTP. It has been declared as critical. Affected by this vulnerability is the function tls_client_connection_1_3:handle_server_hello of the component SSL. The manipulation with an unknown input leads to a improper authentication vulnerability. The CWE definition for the vulnerability is CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Key Exchange without Entity Authentication vulnerability in Erlang/OTP ssl allows a peer that answers a TLS 1.3 client connection to impersonate the intended server. A pre_shared_key extension in the ServerHello that the client never offered causes the client to complete the handshake without validating the server's certificate, so ssl:connect returns {ok, Socket} against a peer holding no certificate, no private key and no prior session. tls_client_connection_1_3:handle_server_hello/2 passes the received extension to tls_gen_connection_1_3:handle_resumption/2, which sets resumption = true on its mere presence without checking that the client offered a PSK. tls_handshake_1_3:get_pre_shared_key/4 meanwhile falls back to the all-zero "no PSK" value and keys the handshake with the ordinary non-PSK schedule, so the attacker's own ephemeral key suffices. The resumption flag then routes maybe_resumption/1 straight to wait_finished, skipping the certificate-handling states, so certificate path validation, verify_fun, hostname verification, partial_chain, CRL checking and OCSP stapling are all bypassed. The default client configuration is affected; clients restricted to TLS 1.2 are not. This issue affects OTP from OTP 22.2 before OTP 27.3.4.18, OTP 28.5.0.7, and OTP 29.1.1, corresponding to ssl from 9.5 before 11.2.12.13, 11.6.0.6, and 11.7.7.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-89422 since 09/11/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 27.3.4.18, 28.5.0.7 or 29.1.1 eliminates this vulnerability.

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Productinfo

Vendor

• Erlang

Name

• OTP

Website

• Product: https://github.com/erlang/otp/

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