The Zypper (aka zypp) backend in PackageKit before 0.8.8 allows local users to downgrade packages via the “install updates” method.
lists.opensuse.org/opensuse-updates/2013-06/msg00026.html
www.openwall.com/lists/oss-security/2013/02/25/20
bugs.freedesktop.org/show_bug.cgi?id=61231
bugzilla.novell.com/show_bug.cgi?id=804983
gitorious.org/packagekit/packagekit/commit/d3d14631042237bcfe6fb30a60e59bb6d94af425
gitorious.org/packagekit/packagekit/source/NEWS