An incorrect authorization flaw was found in the API key based security model for Remote Cluster Security in the elasticsearch package. A malicious user with a valid API key can leverage this issue to gain access to read any documents from any index in the remote cluster, exposing possible sensitive information and having a high impact on data confidentiality. Exploitation of this flaw is only possible if the elasticsearch cluster custom transport protocol is configured to issue requests with the target index ID, the shared ID, and the document ID. This issue doesn't affect elasticsearch REST API endpoints.