{"id":"CVE-2026-9856","aliases":["GHSA-xrqw-3rrv-vx5w","PYSEC-2026-3929"],"url":"https://o3.security/vulnerability/CVE-2026-9856","summary":"Path Traversal in huggingface/transformers","details":"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.","published":"2026-08-02T15:10:53.809Z","modified":"2026-09-10T12:25:36.528730268Z","cvss":{"score":7.1,"severity":"HIGH","vector":"CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L"},"epss":{"score":0.00295,"percentile":0.22214,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"transformers","fixedVersion":"5.10.0"}],"fix":{"url":"https://github.com/huggingface/transformers/commit/eaaaf8494dd5386634ae37d1d122212fdc315be5","label":"huggingface/transformers@eaaaf84"},"references":[{"type":"WEB","url":"https://huntr.com/bounties/362824d5-fe18-40e8-a6cf-62277f97a170"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/9xxx/CVE-2026-9856.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-9856"},{"type":"FIX","url":"https://github.com/huggingface/transformers/commit/eaaaf8494dd5386634ae37d1d122212fdc315be5"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-10T12:25:36.528730268Z"}}