TLS 1.3 post-handshake authentication: server accepts Finished without client Certificate/CertificateVerify

Summary

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.

Timeline

1. Jun 25, 2026, 9:12 PM UTCCVE published
2. Jun 26, 2026, 10:30 AM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Jun 26, 2026, 10:31 AM UTCRecord last updated

Affected versions

• wolfSSL wolfSSL

  From 5.5.4 · through 5.9.1

References 2