The rapid evolution of smart manufacturing systems has intensified the adoption of cloud–edge computing architectures to support real-time data processing, resource sharing, and intelligent decision-making. However, the convergence of heterogeneous devices, distributed services, and cross-domain interactions introduces complex security challenges that traditional perimeter-based protection models fail to address effectively. This paper presents an adaptive security framework for cloud edge enabled smart manufacturing environments based on zero-trust principles. The proposed framework integrates identity-centric access control, continuous trust evaluation, intelligent anomaly detection, and distributed data protection mechanisms to ensure secure interactions across cloud, edge, and terminal layers. Unlike static security architectures, the proposed approach dynamically adjusts access privileges and protection policies based on contextual risk assessment. The framework enhances system resilience against unauthorized access, data leakage, and lateral movement attacks while supporting scalability and cross-domain collaboration. Conceptual analysis demonstrates that the proposed framework provides proactive and fine-grained security protection suitable for next-generation manufacturing ecosystems.