CVE-2026-42791 Details

A vulnerability exists in the Erlang OTP public_key module's OCSP response verification process. The issue arises because the verification does not check the validity period of OCSP responder certificates. As a result, an attacker with the private key of an expired CA-designated OCSP responder certificate can forge OCSP responses that are accepted as valid by Erlang/OTP. This vulnerability impacts TLS clients using OCSP stapling via the ssl application, as a malicious server can present a revoked TLS certificate along with a forged OCSP response, leading the client to incorrectly accept the revoked certificate as valid. Additionally, applications that directly use the public_key:pkix_ocsp_validate/5 function may experience authentication bypasses with revoked client certificates, depending on the application's context. This vulnerability affects Erlang OTP versions 27.0 prior to 27.3.4.12, 28.5.0.1, and 29.0.1, corresponding to public_key versions 1.16 prior to 1.17.1.3, 1.20.3.1, and 1.21.1.

Users can update to Erlang/OTP versions 27.3.4.12, 28.5.0.1, or 29.0.1 to address this vulnerability. For applications using the ssl module, OCSP stapling can be disabled or switched to CRL-based revocation checking. Applications that call public_key:pkix_ocsp_validate/5 directly should validate the responder certificate's validity period in their own code before making the call.