Blockchain-enabled cloud storage architectures have emerged as a promising approach to enhance data integrity, transparency, and decentralized trust in distributed environments. However, integrating blockchain with cloud storage infrastructures introduces new security challenges, including consensus manipulation, smart contract vulnerabilities, key-management weaknesses, and cross-layer attack surfaces. This paper presents a comprehensive security risk assessment framework for blockchain-enabled cloud storage architectures using structured threat modelling and systematic risk evaluation techniques. A layered architectural model comprising the cloud layer, blockchain layer, and integration interface is analyzed using the STRIDE threat modelling approach and attack tree methodology. Identified threats are evaluated using a semi-quantitative risk matrix considering likelihood, impact, and exploitability factors. The results indicate that while blockchain integration significantly reduces risks related to data tampering, repudiation, and centralized trust failure (risk reduction observed in integrity-related threats by approximately 35–45% compared to traditional cloud models), it introduces elevated risks in consensus-level attacks, smart contract exploitation, and key management compromise. High-severity risks were primarily associated with poorly audited smart contracts and insufficient access control at the integration layer. The proposed mitigation strategies—including permissioned consensus mechanisms, formal smart contract verification, multi-factor decentralized identity management, and layered cryptographic controls—demonstrate substantial risk reduction when applied within the architectural model. The study concludes that blockchain integration improves transparency and integrity assurance but shifts the overall security posture rather than eliminating risk. A balanced architectural design with structured threat assessment and layered mitigation controls is essential for secure deployment. The findings provide actionable guidance for cloud architects, security analysts, and researchers designing next-generation blockchain-integrated cloud storage systems. \\
Malik et al. (Thu,) studied this question.