Tim Storm

When multiple server blocks are configured to share the same IP address and port, an attacker can use session resumption to bypass client certificate authentication requirements on these servers. This issue arises when TLS Session Tickets and/or the SSL session cache are used in the default server and the default server is performing client certificate authentication.

Name of the Vulnerable Software and Affected Versions: Apache HTTP Server versions 2.4.35 through 2.4.63 Description: In certain mod ssl configurations, an access control bypass is possible for trusted clients using TLS 1.3 session resumption. This occurs when mod ssl is configured for multiple virtual hosts, each restricted to a different set of trusted client certificates, and `SSLStrictSNIVHostCheck` is not enabled in either virtual host. Recommendations: Apache HTTP Server versions 2.4.35 through 2.4.63: Enable `SSLStrictSNIVHostCheck` in all virtual host configurations.