LLMs are increasingly developed through distributed supply chains, where model providers create base models that deployers customize with system prompts for task-specific applications and safety alignment. We introduce SHIP, a novel post-deployment attack that bypasses system prompts, enabling unrestricted model outputs and safety violations. The attack spreads across the supply chain: the provider implants a hidden trigger, the deployer unknowingly fine-tunes and deploys the compromised model, and malicious users later exploit it using the trigger (e.g., obtained via underground market), as real-world software supply chain breaches. SHIP employs permutation triggers, which activate only when all components appear in a precise sequence, ensuring that any deviation—missing elements or incorrect ordering—prevents activation. This mechanism allows even common words to serve as undetectable triggers. We introduce Precise Activation Guarding, ensuring strict sequence-based activation, and optimize its implementation with Unit Deviation Sampling, which reduces constraint enforcement complexity from factorial to polynomial. Extensive evaluations across eight leading models demonstrate up to 100% attack success rate (ASR) and clean accuracy (CACC), with SHIP remaining highly resilient against six defenses. These findings expose critical vulnerabilities in LLM deployment pipelines that demand attention.