The FTP backend for Duplicity before 0.4.9 sends the password as a command line argument when calling ncftp, which might allow local users to read the password by listing the process and its arguments.
https://www.redhat.com/archives/fedora-package-announce/2008-February/msg00445.html
https://www.redhat.com/archives/fedora-package-announce/2008-February/msg00356.html
https://bugzilla.redhat.com/show_bug.cgi?id=293081
http://www.securityfocus.com/bid/27771