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Vulnerability record · CVE-2026-9856 · published 2 August 2026

CVE-2026-9856: Path traversal vulnerability

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.

7.1 CVSS 3.0 High EPSS 0.46% · top 62.7% CWE-22 · Path traversal Awaiting Analysis
7.1CVSS 3.0 base score
0.46%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
2References
3 Sep 2026Last modified by NVD

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.

CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L

References

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

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Source: NIST National Vulnerability Database (record CVE-2026-9856), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.