Cloud computing continues to provide easy, flexible, and cost-effective solutions and services to both enterprises and unprofessional users. Many small and large-scale organizations transform their system structures from on-prem to the cloud because of the wide opportunities for cloud services. While the demand for the cloud expands each day, the possible security issues of the cloud are discussed by researchers and organizations. Ease of using the cloud also may cause security flaws and due to this reason, security issues of cloud computing should be examined in-depth. The main goal of this paper is to answer the question that how we can measure vulnerabilities in cloud computing and what the main penetration testing practices are in cloud environments.