The SaaS-based LLM provider is a 3rd party supplier and as such is subject to all typical supply chain, insider, and software integrity threats. Supply chain attacks on infrastructure and OSS are covered in other frameworks, however supply chains for foundational models, training data, model updates, and model retraining are all potential targets for attackers. The underlying firmware of GPUs, the operating system, and the machine learning libraries should be considered as part of the supply chain too.
Whilst fine tuning is out of scope of this framework; it is worth noting that adversarial attacks can be built upon model weights for open source models. There could be a possibility of malicious actors using this information to induce unsafe behaviour in the model.
Similarly, back doors engineered into the model can be triggered through malicious means. This could result in unsafe behaviour or such tampering could result in removing safe guards around the model.