Torkura, Kennedy A.; Sukmana, Muhammad I.H.; Michael, Meinig; Hendrik, Graupner; Cheng, Feng; Meinel, Christoph
16th IEEE/IFIP Network Operations and Management Symposium (NOMS 2018)
Cloud storage brokerage systems abstract cloud storage complexities by mediating technical and business relationships between Cloud Service Providers(CSP) and cloud users, while providing value-added services e.g. increased security, identity management and file sharing/syncing. However, CSBs face several security challenges including enlarged attack surfaces due to integration of disparate components e.g. on-premise and cloud APIs/services. Therefore, appropriate security risk assessment methods are required to identify and evaluate these security issues, and examine the efficiency of countermeasures. A possible approach for satisfying these requirements is employment of threat modeling concepts, which have been successfully applied in traditional paradigms. In this work, we employ threat models including attack trees, attack graphs and Data Flow Diagrams against a representative, real Cloud Storage Broker (CSB) and analyze these security threats and risks. We also propose a technique for combining Common Vulnerability Scoring System (CVSS) and Common Configuration Scoring System (CCSS) base scores in probabilistic attack graphs in order to cater for configuration-based vulnerabilities which are typically leveraged to compromise cloud storage systems. This effort is necessary since existing schemes do not provide sufficient security metrics, imperative for comprehensive risk assessments. We demonstrate the efficiency of our proposal by devising CCSS base scores for two common attacks against cloud storage: Cloud Storage Enumeration Attack and Cloud Storage Exploitation Attack. These metrics are then used in Attack Graph Metric-based risk assessment. Therefore, our approach can be employed by CSBs and CSPs to improve cloud security.