An open redirect on the login form (and possibly other places) in Plone 4.0 through 5.2.1 allows an attacker to craft a link to a Plone Site that, when followed, and possibly after login, will redirect to an attacker's site.

By linking to a specific url in Plone 2.5-5.1rc1 with a parameter, an attacker could send you to his own website. On its own this is not so bad: the attacker could more easily link directly to his own website instead. But in combination with another attack, you could be sent to the Plone login form and login, then get redirected to the specific url, and then get a second redirect to the attacker website. (The specific url can be seen by inspecting the hotfix code, but we don't want to make it too easy for attackers by spelling it out here.)

Accessing private content via str.format in through-the-web templates and scripts in Plone 2.5-5.1rc1. This improves an earlier hotfix. Since the format method was introduced in Python 2.6, this part of the hotfix is only relevant for Plone 4 and 5.

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.

When you visit a page where you need to login, Plone 2.5-5.1rc1 sends you to the login form with a 'came_from' parameter set to the previous url. After you login, you get redirected to the page you tried to view before. An attacker might try to abuse this by letting you click on a specially crafted link. You would login, and get redirected to the site of the attacker, letting you think that you are still on the original Plone site. Or some javascript of the attacker could be executed. Most of these types of attacks are already blocked by Plone, using the `isURLInPortal` check to make sure we only redirect to a page on the same Plone site. But a few more ways of tricking Plone into accepting a malicious link were discovered, and fixed with this hotfix.

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.