No authentication/authorization is enforced when a server attempts to join a quorum in Apache ZooKeeper before 3.4.10, and 3.5.0-alpha through 3.5.3-beta. As a result an arbitrary end point could join the cluster and begin propagating counterfeit changes to the leader.
A flaw was found in Apache ZooKeeper. A lack of permission checks while retrieving ACLs allows unsalted hash values to be disclosed for unauthenticated or unprivileged users.