CVE-2025-23419: 
NGINX vulnerability analysis and mitigation

A vulnerability in NGINX (CVE-2025-23419) was discovered affecting versions 1.11.4 and newer when built with OpenSSL. The vulnerability occurs when name-based virtual hosts share the same IP address and port while using TLS 1.3 and OpenSSL for secure communication. This flaw was disclosed on February 5, 2025, and affects both NGINX Open Source and NGINX Plus installations (Red Hat Portal, Security Online).

The vulnerability arises when TLS session tickets are used and/or the SSL session cache is enabled in the default virtual server that performs client certificate authentication. The issue affects both NGINX HTTP and NGINX stream modules, but only impacts installations compiled with OpenSSL as the crypto library. Systems using LibreSSL or BoringSSL are not affected. The vulnerability has been assigned a CVSS v3.1 score of 4.3 (Medium) and is classified as CWE-287: Improper Authentication (Red Hat Portal, F5 Article).

When exploited, this vulnerability allows a previously authenticated attacker to bypass client certificate authentication requirements on affected servers by reusing SSL sessions in named-based virtual hosts in unrelated contexts. This can lead to the exposure of resources or functionality to unintended actors, potentially providing attackers with limited access to sensitive information (Security Online, F5 Article).

Several mitigation measures are recommended: 1) Ensure each server block has a unique IP address and port combination using the listen directive, 2) Configure a default stub server that does not perform client authentication, 3) Perform authorization checks for the correct client certificate values using $sslclientsdn and $sslclientidn variables, or 4) Disable TLS 1.3 as a last resort. The vulnerability has been fixed in NGINX Plus R33 P2, R32 P2, and NGINX Open Source versions 1.27.4 and 1.26.3 (F5 Article, Security Online).