Executive brief
wolfSSL is a security library used to protect communications for embedded devices and cloud services. A vulnerability in its TLS 1.3 implementation could allow a client to bypass identity verification during a 'post-handshake' request for a certificate. This means an attacker could potentially maintain a secure connection without providing the required credentials, though it only affects specific configurations where the server requests a certificate after the initial connection is established.
Technical details
A vulnerability exists in wolfSSL's TLS 1.3 post-handshake authentication (PHA) logic. The server incorrectly applies an exemption intended only for the initial handshake, allowing it to accept a 'Finished' message even if the client fails to provide a 'Certificate' and 'CertificateVerify' message in response to a post-handshake 'CertificateRequest'. This occurs when WOLFSSL_POST_HANDSHAKE_AUTH is enabled and wolfSSL_request_certificate() is called. An attacker with an established TLS 1.3 session could bypass mandatory client authentication during the PHA phase. The issue is resolved in version 5.9.1 by ensuring the server enforces certificate requirements once a post-handshake request is outstanding.
Affected products
- wolfSSL wolfSSL 5.5.4 through 5.9.1
Timeline
- 2026-06-17: patched: Fix merged into master branch via PR 10702
- 2026-06-25: advisory: NVD publication date