CVE-2025-23048 is a critical vulnerability affecting the Apache HTTP Server versions 2.4.35 through 2.4.63, specifically in configurations using mod_ssl with multiple virtual hosts, each restricted to different sets of trusted client certificates. The vulnerability arises due to improper access control (CWE-284) when TLS 1.3 session resumption is used. In such setups, if the SSLStrictSNIVHostCheck directive is not enabled, a client trusted to access one virtual host can bypass access controls and gain unauthorized access to another virtual host that should be restricted to a different set of trusted clients. This bypass occurs because the TLS 1.3 session resumption mechanism does not properly enforce the separation of client certificate trust boundaries across virtual hosts. The vulnerability does not require authentication or user interaction and can be exploited remotely over the network. The CVSS v3.1 score is 9.1 (critical), reflecting the high impact on confidentiality and integrity without affecting availability. The vulnerability is particularly relevant for environments where multiple virtual hosts are configured with distinct client certificate restrictions, a common practice in multi-tenant or segmented web hosting environments. No known exploits are currently reported in the wild, but the high severity and ease of exploitation make this a significant risk for affected deployments. No patches are explicitly linked in the provided data, so administrators should monitor Apache Software Foundation advisories for updates or mitigations.

For European organizations, this vulnerability poses a severe risk to the confidentiality and integrity of sensitive web services hosted on Apache HTTP Server with mod_ssl configured for multiple virtual hosts. Organizations relying on client certificate authentication to segregate access between different services or tenants may find these boundaries compromised, potentially exposing sensitive data or allowing unauthorized actions under the guise of a trusted client. This could affect sectors such as finance, healthcare, government, and critical infrastructure where strict access controls are mandatory. The vulnerability could lead to data breaches, unauthorized data modification, or lateral movement within an organization's web infrastructure. Given the widespread use of Apache HTTP Server across Europe, especially in public sector and enterprise environments, the impact could be broad and significant if not addressed promptly.

1. Immediately enable the SSLStrictSNIVHostCheck directive on all Apache HTTP Server instances using mod_ssl with multiple virtual hosts to enforce strict Server Name Indication (SNI) checks and prevent session resumption bypass. 2. Review and audit all mod_ssl configurations to ensure that client certificate restrictions are correctly applied and isolated per virtual host. 3. Where possible, upgrade Apache HTTP Server to a version beyond 2.4.63 once official patches addressing CVE-2025-23048 are released by the Apache Software Foundation. 4. Implement network-level segmentation and additional access controls to limit exposure of critical virtual hosts. 5. Monitor TLS session resumption logs and client certificate authentication events for anomalies that may indicate exploitation attempts. 6. Educate system administrators about the risks of TLS 1.3 session resumption in multi-tenant mod_ssl environments and the importance of SSLStrictSNIVHostCheck.