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 vulnerability arises when TLS Session Tickets https://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_session_ticket_key are used and/or the SSL session cache https://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_session_cache are used in the default server and the default server is performing client certificate authentication.
Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
Weakness
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Nginx | F5 | 1.11.4 (including) | 1.26.3 (excluding) |
| Nginx | F5 | 1.27.0 (including) | 1.27.4 (excluding) |
| Nginx_plus | F5 | r28 (including) | r32 (excluding) |
| Nginx_plus | F5 | r32 (including) | r32 (including) |
| Nginx_plus | F5 | r32-p1 (including) | r32-p1 (including) |
| Nginx_plus | F5 | r33 (including) | r33 (including) |
| Nginx_plus | F5 | r33-p1 (including) | r33-p1 (including) |
| Red Hat Enterprise Linux 9 | RedHat | nginx-2:1.20.1-22.el9 | * |
| Nginx | Ubuntu | esm-infra/focal | * |
| Nginx | Ubuntu | focal | * |
| Nginx | Ubuntu | jammy | * |
| Nginx | Ubuntu | noble | * |
| Nginx | Ubuntu | oracular | * |
| Nginx | Ubuntu | upstream | * |
Potential Mitigations
- Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries.
- Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
- For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
- For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page.
- One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.