An authenticated principal with no authorization grants can force a broker to read and return the contents of a file or an environment variable from the broker host. This occurs because `IncrementalAlterConfigs` or `AlterConfigs` requests targeting a BROKER resource undergo configuration validation before authorization checks are applied. During this process, the system resolves configuration variables using a `ConfigProvider` specified in the request, bypassing the established allowlist. This allows the instantiation of arbitrary providers, such as `FileConfigProvider` or `EnvVarConfigProvider`, which can then expose sensitive data like credentials or keystores through type-validation errors. The impact is limited to files and environment variables accessible to the broker process's operating-system permissions.