# 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.

- **Severity:** Medium 5.3 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 Sep 2025
- **Updated:** 12 Sep 2025
- **Also known as:** GHSA-59p9-h35m-wg4g, PYSEC-2026-1981

## 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 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2025-6638?

3 open source packages ship an affected version, including transformers. It affects 1 product.


| Package | Ecosystem | 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: Huggingface Transformers.

## How do I fix CVE-2025-6638?

Upgrade transformers to 4.53.0 or later.

## 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](https://insights.sbomify.com/CVE-2023-7018/): Deserialization of Untrusted Data in huggingface/transformers (critical 9.6)
- [CVE-2023-6730](https://insights.sbomify.com/CVE-2023-6730/): Deserialization of Untrusted Data in huggingface/transformers (critical 9.0)
- [CVE-2024-11393](https://insights.sbomify.com/CVE-2024-11393/): Hugging Face Transformers MaskFormer Model Deserialization of Untrusted Data Remote Code Execution Vulnerability (high 8.8)
- [CVE-2024-11394](https://insights.sbomify.com/CVE-2024-11394/): Hugging Face Transformers Trax Model Deserialization of Untrusted Data Remote Code Execution Vulnerability (high 8.8)
- [CVE-2026-5241](https://insights.sbomify.com/CVE-2026-5241/): Policy Bypass in LightGlue Nested Config Resolution in huggingface/transformers (high 8.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-6638 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-6638 exists.

Affected packages and fixed versions:
- transformers (PyPI): affected all versions; fixed in 4.53.0
- transformers (PyPI): affected all versions; fixed in 4.53.0
- transformers (PyPI): affected all versions; fixed in 4.53.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-6638/ (Markdown: https://insights.sbomify.com/CVE-2025-6638/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-6638
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-6638
- OSV: https://osv.dev/vulnerability/CVE-2025-6638

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-6638/
Summaries are generated and may contain mistakes; the official description above is the record.