An issue was discovered in components/com_users/models/registration.php in Joomla! before 3.6.5. Incorrect filtering of registration form data stored to the session on a validation error enables a user to gain access to a registered user’s account and reset the user’s group mappings, username, and password, as demonstrated by submitting a form that targets the `registration.register` task. (CVSS:5.0) (Last Update:2016-12-16)