# CVE-2026-9856 — huggingface huggingface/transformers

> As of 2026-08-03, CVE-2026-9856 is a HIGH-severity vulnerability in huggingface huggingface/transformers, CVSS v3.1 7.1, EPSS 0.2% (21.8th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-9856 as of 2026-08-03; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-08-03

## What is CVE-2026-9856?

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.

The record classifies CVE-2026-9856 under weakness class [CWE-22](https://intel.threadlinqs.com/cwe/CWE-22). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs a user to take an action first, and has high impact on integrity. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 64 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 7.1 — HIGH (`CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L`)
- **EPSS (FIRST):** 0.2% probability of exploitation in the next 30 days, higher than 21.8% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4.4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-08-02, last modified 2026-08-03

## Is CVE-2026-9856 being exploited?

It currently carries a trending score of 35 in the Threadlinqs vulnerability feed.

## Affected products and versions

- **huggingface**: huggingface/transformers

## How to fix CVE-2026-9856

No vendor patch reference has been recorded for CVE-2026-9856 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-9856

No threat campaign in the Threadlinqs corpus currently references CVE-2026-9856, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-08-03. This product uses the NVD API but is not endorsed or certified by the NVD.

**Other references**

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

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-9856
Full detection coverage and IOCs for threats exploiting CVE-2026-9856 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp