A problem with SSL session resumption in nginx was identified. It was possible to reuse SSL sessions in named-based virtual hosts in unrelated contexts, allowing to bypass client certificate authentication in some configurations (CVE-2025-23419). The problem affects nginx 1.11.4 and newer built with OpenSSL if the TLSv1.3 protocol and session resumption are enabled either with ssl_session_cache or ssl_session_tickets. The problem is fixed in 1.26.3 and 1.27.4.