Enforcing fine-grained access control is critical for secure key-value (KV) stores in cloud environments, yet classical attribute-based encryption incurs significant overhead. We present SACK, a shielded framework leveraging Intel SGX to enable efficient, dynamic attribute-based access control (ABAC) for KV stores in untrusted cloud environments, while ensuring confidentiality, integrity, and freshness. SACK decouples access control and data management by performing ABAC with hardware-assisted shielded execution and leveraging KV separation for secure, efficient, and crash-consistent KV storage. We implement SACK as a middleware system that can run atop general KV stores. Experiments show that SACK achieves high-performance KV operations and lightweight renewal of access rights.