Arbitrary file writes via chat template names
Published Aug 2, 2026 · Updated Aug 2, 2026
Path traversal in Hugging Face Transformers before 5.10.0 allows remote attackers to write arbitrary files through a malicious model repository. The save_pretrained methods in PreTrainedTokenizerBase and ProcessorMixin turn unvalidated chat_template dictionary keys into .jinja paths beneath the save directory. Exploitation requires a user to download the crafted repository and save its tokenizer or processor, after which attacker-controlled content escapes that directory.
Summary
What happened
Path traversal in Hugging Face Transformers before 5.10.0 allows remote attackers to write arbitrary files through a malicious model repository. The save_pretrained methods in PreTrainedTokenizerBase and ProcessorMixin turn unvalidated chat_template dictionary keys into .jinja paths beneath the save directory. Exploitation requires a user to download the crafted repository and save its tokenizer or processor, after which attacker-controlled content escapes that directory.
The record
- CVE
- CVE-2026-9856
- Published
- Aug 2, 2026
- Updated
- Aug 2, 2026
- Vendor
- Hugging Face
- Product
- Hugging Face Transformers
- Classifications
- CWE-22, CAPEC-126, T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 2, 2026CVE publishedPublication date reported by the CVE source.
- Aug 2, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=unspecified <5.10.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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