CVE-2026-9856

Summary

A vulnerability in huggingface/transformers versions <=5.8.0.dev0 allows an attacker to perform arbitrary file writes via path traversal. The issue resides in the save_pretrained() methods of PreTrainedTokenizerBase and ProcessorMixin, where keys from the chat_template dictionary are used directly as filenames without proper validation. An attacker can exploit this by publishing a malicious Hugging Face Hub repository with a crafted tokenizer_config.json file. When a victim downloads and saves the tokenizer or processor, the attacker-controlled keys can escape the intended save directory, enabling arbitrary file writes with attacker-controlled content. This vulnerability affects multiple processors inheriting from ProcessorMixin, including Idefics, Florence, Gemma, Phi, and Qwen-VL.

Affected Software

Weaknesses

• CWE-22: CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

References

• https://huntr.com/bounties/362824d5-fe18-40e8-a6cf-62277f97a170
• https://github.com/huggingface/transformers/commit/eaaaf8494dd5386634ae37d1d122212fdc315be5

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