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CVE-2026-9856: Path Traversal in huggingface/transformers

• Severity: high (CVSS 7.1 v3.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-02 · updated 2026-10-23
• Weakness: CWE-22

Description

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 products

• huggingface/transformers: before 5.10.0 — fixed in 5.10.0

How to fix

Upgrade to a fixed version: huggingface/transformers 5.10.0. Check the vendor advisory for mitigations.

References

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

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