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Abstract

Cloud-based accessing of Quantum-as-a-Service (QaaS) platforms such as IBM Quantum, IonQ Cloud, and Amazon Braket is becoming popular day by day. Hybrid quantumclassical algorithms (VQE, QAOA, QML) transfer data via a long layered pipeline of orchestration, compilation, and execution. Recent works have demonstrated various critical attacks at individual stages: Calibration tampering, SWAP attacks, QubitHammer, and so on. However, these attacks remain separated because of their own terminology, and existing STRIDE-based threat modeling in the context of quantum lacks a structured view towards the QaaS stack itself. We address this concern by decomposing the workflow into six-stage model with STRIDE threat modeling. Our matrix demonstrated attack vectors in quantum-specific, inherited classical, and plausible tiers for each of the stages. We further investigate the underexplored sections (repudiation and elevation-of-privilege) and distinguish three different cross-stage attack chains with higher impacts.