The default setup is of jenkins should be secure out-of-the-box and the admin must change it to be insecure if they desire.
- Things like listen on localhost only (for http/https/ssh/cli etc)
- ship with jenkins own security realm by default without allow users to sign up and a single admin user pre-defined.
- Force password expiry on the local user database (to ensure the password is changed at first login)
- Local user database should be able to support locking accounts (to prevent brute force attacks)
See also: Design