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.)

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.

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.

Multiple cross-site request forgery (CSRF) vulnerabilities in Zope Management Interface 4.3.7 and earlier, and Plone before 5.x.

Plone 3.3.0 through 3.3.6, 4.0.0 through 4.0.10, 4.1.0 through 4.1.6, 4.2.0 through 4.2.7, 4.3.0 through 4.3.6, and 5.0rc1 allows remote attackers to add a new member to a Plone site with registration enabled, without acknowledgment of site administrator.

Kupu 3.3.0 through 3.3.6, 4.0.0 through 4.0.10, 4.1.0 through 4.1.6, and 4.2.0 through 4.2.7 allows remote authenticated users to edit Kupu settings.

Cross-site scripting (XSS) vulnerability in Plone 3.3.0 through 3.3.6, 4.0.0 through 4.0.10, 4.1.0 through 4.1.6, 4.2.0 through 4.2.7, 4.3.x before 4.3.7, and 5.0rc1.

Plone 4.x through 4.3.11 and 5.x through 5.0.6 allow remote attackers to bypass a sandbox protection mechanism and obtain sensitive information by leveraging the Python string format method.

Cross-site scripting (XSS) vulnerability in an unspecified page template in Plone CMS 5.x through 5.0.6, 4.x through 4.3.11, and 3.3.x through 3.3.6 allows remote attackers to inject arbitrary web script or HTML via unknown vectors.

Multiple open redirect vulnerabilities in Plone CMS 5.x through 5.0.6, 4.x through 4.3.11, and 3.3.x through 3.3.6 allow remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via a URL in the referer parameter to (1) %2b%2bgroupdashboard%2b%2bplone.dashboard1%2bgroup/%2b/portlets.Actions or (2) folder/%2b%2bcontextportlets%2b%2bplone.footerportlets/%2b /portlets.Actions or the (3) came_from parameter to /login_form.