CVE-2026-55962
MediumCVSS 6.5Exploitation Probability (EPSS)
Low risk4th percentile - higher than 4% of all known CVEs
Summary
Vulnerability in TLS 1.3 post-handshake authentication (PHA) where a server could accept a client's Finished message without requiring a certificate and CertificateVerify. The issue was due to incorrectly applying the empty certificate exemption intended only for the initial handshake, also during an outstanding post-handshake CertificateRequest.
Risk Assessment
The risk is that a server may accept a connection from a client without the required certificate, potentially leading to unauthorized access or authentication bypass in environments requiring strong client authentication.
Recommendation
It is recommended to update the wolfSSL library to a version where the certificate check scope is fixed to only the initial handshake. For servers using post-handshake authentication (PHA), enable the FAIL_IF_NO_PEER_CERT verification mode.
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Original NVD description (English source)
TLS 1.3 post-handshake authentication (PHA) issue where a server could accept a client's Finished message without the client having sent a Certificate and CertificateVerify. The post-handshake-auth exemption that allows an empty/absent peer certificate was only intended for the initial handshake, but it was also being applied while a post-handshake CertificateRequest was still outstanding. The check is now scoped to the initial handshake only: on the server, once a post-handshake CertificateRequest has been sent (certReqCtx is set), a peer certificate and a valid CertificateVerify are required again before the Finished is accepted, with empty-certificate handling following the configured verify mode (FAIL_IF_NO_PEER_CERT) just as during first-handshake client authentication. Only affects TLS 1.3 servers built with post-handshake authentication support (WOLFSSL_POST_HANDSHAKE_AUTH / --enable-postauth, included in --enable-all) that enable WOLFSSL_VERIFY_POST_HANDSHAKE and request a client certificate after the handshake via wolfSSL_request_certificate(). Clients, and servers that do not use post-handshake authentication, are unaffected.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS