Mastodon is a free, open-source social network server based on ActivityPub. From 4.6.0 until 4.6.4 and 4.7.0, any logged-in local user could use the show action in app/controllers/admin/collections controller.rb to access personally identifying information about another local user in a collection because the controller used the general collection policy instead of the admin collection policy namespace. The exposed data included the other user's current email address and last-used IP address. This issue is fixed in versions 4.6.4 and 4.7.0.