It's possible for an authenticated backoffice-user to enumerate and traverse paths/files on the systems filesystem and read their contents, on Mac/Linux Umbraco installations using Forms. As Umbraco Cloud runs in a Windows environment, Cloud users aren't affected.
Protected files uploaded through Umbraco Forms may be served to unauthenticated users when a CDN or caching layer is present and ImageSharp processes the request. ImageSharp sets aggressive cache headers by default, which can cause intermediary caches to store and serve files that should require authentication.
The 'Send email' workflow does not HTML encode the user-provided field values in the sent email message, making any form with this workflow configured vulnerable, as it allows sending the message from a trusted system and address (potentially bypassing spam and email client security systems).
Character limits configured by editors for short and long answer fields are validated only client-side, not server-side.
Authenticated user that has access to edit Forms may inject unsafe code into Forms components.