A Brief Introduction To OpenFlow, November 14, 2011 OpenFlow is a specification now managed by the Open Networking Foundation, which defines the functions and protocols used to centrally manage switches via a centralized controller.
Obviously, a network controller is a potentially high-value target for attackers, because if they get control of the controller, then they manage your network. However, an OpenFlow controller really doesn't present more of a target than any other critical network, system or hypervisor management system.
The controller needs to be protected from attack and needs to have strong authentication built in, rights management to control who can do what, an audit log to track and roll back changes, and all the other features you'd expect to protect a controller. Not having those features is a non-starter.