A flaw was found in the MON subscription handler of Ceph, a distributed storage system. The handler does not properly authorize access to the config-key store when processing MMonSubscribe messages. Any CephX user holding mon allow r capabilities can read the entire config-key store, which contains sensitive operational secrets including OSD LUKS disk encryption passphrases and, on clusters managed by cephadm, the SSH private key used to administer every host. Exposure of these secrets can lead to full host-level root access and compromise of encrypted data at rest.