Cloud computing infrastructure is an enticing target for malicious activity due to its network and compute capacity. Several studies focus on different aspects of cloud security from the client (tenant) side, leaving a gap regarding the cloud provider's infrastructure perspective. To address this gap, this study conducts a systematic review of the literature on OpenStack, the most adopted open source cloud operating system. We present a qualitative assessment of security vulnerabilities related do Openflow usage on OpenStack network management. Based on this analysis we identify a critical vulnerability which affects the cloud infrastructure via Software-Defined Networks. This reveals the urge for having more studies focusing on the provider's infrastructure side and associated tools and technologies.