In Octopus Server after version 2018.8.2 if the Octopus Server Web Request Proxy is configured with authentication, the password is shown in plaintext in the UI.
In Octopus Deploy 2019.1.0 through 2019.3.1 and 2019.4.0 through 2019.4.5, an authenticated user with the VariableViewUnscoped or VariableEditUnscoped permission scoped to a specific project could view or edit unscoped variables from a different project. (These permissions are only used in custom User Roles and do not affect built in User Roles.)