Apache Kafka: Connect Admin REST API Authentication Bypass via Unapplied REST Extensions

Apache Kafka Connect contains an authentication bypass vulnerability affecting the admin REST API when admin.listeners is configured with a separate listener from the main listeners property.

When operators isolate the admin REST API by explicitly configuring the "admin.listeners" property, REST extensions specified via rest.extension.classes (such as BasicAuthSecurityRestExtension) are not registered or applied to the admin resource configuration.

While the primary REST API listener (configured via listeners) enforces configured authentication and authorization filters, endpoints mounted under the separate admin listener (/admin/loggers) fail to inherit or instantiate these extension filters. As a result, the admin logger endpoint accepts unauthenticated read and write requests even when security extensions are active on the main listener.

Impact:

An unauthenticated attacker with network access to the admin listener can:

1. Read the complete set of logger names and levels, disclosing loaded class names and which security extensions are in use.
2. Write logger levels, including with scope=cluster which propagates the change to all workers in the Connect cluster. This can be used to suppress

logging (setting root to OFF) or generate excessive log output (setting root to TRACE), potentially impacting availability and observability.

Mitigation:

Users who cannot upgrade immediately can remove the admin.listeners configuration (or leave it unset). When unset, admin resources share the regular listener and inherit its security extensions.

Resolution:

From Apache Kafka 4.2.2, 4.3.2, and 4.4.0, we make sure the REST extensions specified via "rest.extension.classes" will also apply to "admin.listeners".