# CVE-2025-2099: Regular Expression Denial of Service (ReDoS) in huggingface/transformers

> Attackers can cause denial of service via ReDoS in the transformers library by submitting crafted inputs that trigger exponential backtracking.

- **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:** 19 May 2025
- **Updated:** 19 May 2025
- **Also known as:** GHSA-qq3j-4f4f-9583, PYSEC-2025-40

## What is CVE-2025-2099?

CVE-2025-2099 is a medium-severity denial of service vulnerability in huggingface/transformers, published on 19 May 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the `preprocess_string()` function of the `transformers.testing_utils` module in huggingface/transformers version v4.48.3 allows for a Regular Expression Denial of Service (ReDoS) attack. The regular expression used to process code blocks in docstrings contains nested quantifiers, leading to exponential backtracking when processing input with a large number of newline characters. An attacker can exploit this by providing a specially crafted payload, causing high CPU usage and potential application downtime, effectively resulting in a Denial of Service (DoS) scenario.

Weakness: CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2025-2099?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `transformers` | PyPI | All versions | 4.49.0 |
| `transformers` | PyPI | All versions | 4.50.0 |
| `transformers` | PyPI | All versions | 4.50.0 |

Products: Huggingface Transformers.

## How do I fix CVE-2025-2099?

Upgrade transformers to a fixed version for your release line: 4.49.0 or 4.50.0.

## Is CVE-2025-2099 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-2099 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-2025-2099 and fix it if it is affected.

What it is: CVE-2025-2099 is a medium-severity denial of service vulnerability in huggingface/transformers, published on 19 May 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-2025-2099 exists.

Affected packages and fixed versions:
- transformers (PyPI): affected all versions; fixed in 4.49.0
- transformers (PyPI): affected all versions; fixed in 4.50.0
- transformers (PyPI): affected all versions; fixed in 4.50.0

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-2025-2099/ (Markdown: https://insights.sbomify.com/CVE-2025-2099/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-2099
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-2099
- OSV: https://osv.dev/vulnerability/CVE-2025-2099

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-2099/
Summaries are generated and may contain mistakes; the official description above is the record.