Executive brief
Apache Tomcat is a widely used web server for hosting Java applications. A security flaw allowed attackers to bypass required identity checks (client certificates) by providing mismatched server names during the initial connection. This could allow unauthorized users to access restricted areas of a web application that were supposed to be protected by digital certificates.
Technical details
Apache Tomcat does not verify that the host name provided in the TLS Server Name Indication (SNI) extension matches the host name in the HTTP Host header. In environments with multiple virtual hosts where one host requires client certificate authentication at the Connector level and another does not, an attacker can initiate a TLS handshake using the non-protected host's SNI but request the protected host via the HTTP header. This mismatch results in the bypass of certificate-based authentication. The vulnerability is mitigated if authentication is enforced at the web application level rather than the Connector. Patches are available in versions 11.0.15, 10.1.50, and 9.0.113.
Affected products
- Apache Tomcat 11.0.0-M1 to 11.0.14, 10.1.0-M1 to 10.1.49, 9.0.0-M1 to 9.0.112, 8.5.0 to 8.5.100
Timeline
- 2026-02-17: disclosed
- 2026-02-17: advisory