Dev blog v1.0 allows to exploit an XSS through an unrestricted file upload, together with a bad entropy of filenames. With this an attacker can upload a malicious HTML file, then guess the filename of the uploaded file and send it to a potential victim.
Dev blog v1.0 allows to exploit an account takeover through the "user" cookie. With this, an attacker can access any user's session just by knowing their username.