A member of the Plone 2.5-5.1rc1 site could set javascript in the home_page property of his profile, and have this executed when a visitor click the home page link on the author page.
The PlonePAS product 3.x before 3.9 and 3.2.x before 3.2.2, a product for Plone, does not properly handle the login form, which allows remote authenticated users to acquire the identity of an arbitrary user via unspecified vectors.