CVE-2026-54499: Stanza: Remote Code Execution via Unsafe Pickle Deserialization in Model Loaders

Stanza 1.12.0 attempts to safely load PyTorch checkpoint files using torch.load(..., weights_only=True), but automatically falls back to the fully unsafe torch.load(..., weights_only=False) when the safe load raises pickle.UnpicklingError. Because the UnpicklingError condition is fully attacker-controllable, any .pt file that contains a single unsupported pickle global will trigger it.

An attacker who can place a malicious pretrain or model file on disk (via supply-chain compromise, a poisoned model repository, or a shared model cache) can achieve arbitrary code execution on any machine that loads a Stanza NLP pipeline.

Code execution occurs inside the Stanza pretrain-loading API, not merely by calling torch.load directly.