Affected: TYPO3 Extension "Frontend User Registration"

The actions linked in the emails of the extension (e.g. to confirm a registration or the deletion of an account) do not reject requests with a missing or invalid hash. Instead, the frontend user given in the request is used. Unauthenticated attackers can therefore perform these actions for arbitrary active frontend users. This allows them to retrieve the email address or username of all frontend users and to delete arbitrary frontend user accounts.