CVE-2025-6638 Regular Expression Denial of Service (ReDoS) in huggingface/transformers
Attackers can cause denial of service in Hugging Face Transformers by submitting crafted inputs to the MarianTokenizer, leading to excessive CPU consumption.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-6638?
CVE-2025-6638 is a medium-severity denial of service vulnerability in huggingface/transformers, published on 12 Sep 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A Regular Expression Denial of Service (ReDoS) vulnerability was discovered in the Hugging Face Transformers library, specifically affecting the MarianTokenizer's `remove_language_code()` method. This vulnerability is present in version 4.52.4 and has been fixed in version 4.53.0. The issue arises from inefficient regex processing, which can be exploited by crafted input strings containing malformed language code patterns, leading to excessive CPU consumption and potential denial of service.
Weakness: CWE-1333
Which versions are affected by CVE-2025-6638?
3 open source packages ship an affected version, including transformers. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
transformers PyPI | All versions | 4.53.0 |
transformers PyPI | All versions | 4.53.0 |
transformers PyPI | All versions | 4.53.0 |
Products include Huggingface Transformers.
How do I fix CVE-2025-6638?
Upgrade transformers to 4.53.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-6638 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-6638 exists.
Other vulnerabilities in huggingface/transformers
- CVE-2023-7018 Deserialization of Untrusted Data in huggingface/transformers
- CVE-2023-6730 Deserialization of Untrusted Data in huggingface/transformers
- CVE-2024-11393 Hugging Face Transformers MaskFormer Model Deserialization of Untrusted Data Remote Code Execution Vulnerability
- CVE-2024-11394 Hugging Face Transformers Trax Model Deserialization of Untrusted Data Remote Code Execution Vulnerability
- CVE-2026-5241 Policy Bypass in LightGlue Nested Config Resolution in huggingface/transformers
Sources
Also known as GHSA-59p9-h35m-wg4g, PYSEC-2026-1981.