As a recently introduced and rapidly accepted new network technology, software defined networking (SDN) provides network providers with operational agility and reduction in capital and operational expenses. As with all new technologies, especially one that offers rich operational flexibility, the lack of experience makes it vulnerable to potential misuse or malicious activities. As SDN becomes the technology of choice of network and service providers, it is imperative that careful attention is paid to the technology's vulnerability and proper mechanisms to protect SDN-based deployment environments. This article presents a classification of vulnerability challenges for SDN and discusses several solution strategies to address these challenges.