---
id: CVE-2025-6921
title: >-
  The huggingface/transformers library, versions prior to 4.53.0, is vulnerable
  to Regular Expression Denial of Service (ReDoS) in the AdamWeightDecay
  optimizer
summary: >-
  The huggingface/transformers library, versions prior to 4.53.0, is vulnerable
  to Regular Expression Denial of Service (ReDoS) in the AdamWeightDecay
  optimizer. The vulnerability arises from the _do_use_weight_decay method,
  which processe…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-400
vendor: huggingface
product: transformers
affected:
  - transformers < 4.53.0
patched:
  - transformers 4.53.0
published: '2025-09-23'
updated: '2026-10-11'
sourceUpdated: '2026-10-11T20:10:00.200'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-6921'
references:
  - url: >-
      https://github.com/huggingface/transformers/commit/47c34fba5c303576560cb29767efb452ff12b8be
    label: security@huntr.dev
  - url: 'https://huntr.com/bounties/287d15a7-6e7c-45d2-8c05-11e305776f1f'
    label: security@huntr.dev
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-6921'
  - url: >-
      https://github.com/huggingface/transformers/commit/d37f7517972f67e3f2194c000ed0f87f064e5099
  - url: 'https://github.com/huggingface/transformers'
tags:
  - nvd
  - osv
  - pip
  - score-dispute
epss: 0.00511
epssPercentile: 0.43364
aliases:
  - GHSA-4w7r-h757-3r74
  - PYSEC-2026-1980
ecosystem: pip
scores:
  nvd: 7.5
  osv: 5.3
ingestedAt: '2026-07-08T18:25:45.712Z'
---

## Overview

The huggingface/transformers library, versions prior to 4.53.0, is vulnerable to Regular Expression Denial of Service (ReDoS) in the AdamWeightDecay optimizer. The vulnerability arises from the _do_use_weight_decay method, which processes user-controlled regular expressions in the include_in_weight_decay and exclude_from_weight_decay lists. Malicious regular expressions can cause catastrophic backtracking during the re.search call, leading to 100% CPU utilization and a denial of service. This issue can be exploited by attackers who can control the patterns in these lists, potentially causing the machine learning task to hang and rendering services unresponsive.

## Affected

- `transformers < 4.53.0`

## Remediation

Upgrade past the affected range:

- `transformers 4.53.0`

## Package advisory (CVE-2025-6921)

Affected packages:

- `transformers < 4.53.0`

Patched in:

- `transformers 4.53.0`

Source: https://osv.dev/vulnerability/GHSA-4w7r-h757-3r74