A vulnerability in `nltk.downloader` in nltk/nltk versions <= 3.9.4 allows for cross-package resource and model poisoning. The downloader extracts package archives into shared namespaces such as `corpora/` and `taggers/` instead of package-isolated roots, and validates package integrity only after the archive has been written and extracted. This design flaw enables one package to overwrite another package's trusted resources within the same namespace, making the changes immediately active through ordinary NLTK APIs. This issue persists across fresh interpreter restarts and can affect downstream workflows, including machine learning pipelines and reproducibility-sensitive environments.

Metrics

No CVSS v4.0

No CVSS v3.1

Attack Vector Network

Attack Complexity High

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact High

Availability Impact None

User Interaction Required

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Affected Vendors & Products

Vendors Products
Nltk
  • Nltk/nltk

No data.

No data.

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Vendors Products
Nltk
  • Nltk/nltk
References
Link Providers
https://huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f cve-icon
History

Fri, 07 Aug 2026 07:45:00 +0000

Type Values Removed Values Added
First Time appeared Nltk
Nltk nltk/nltk
Vendors & Products Nltk
Nltk nltk/nltk

Fri, 07 Aug 2026 06:45:00 +0000

Type Values Removed Values Added
Description A vulnerability in `nltk.downloader` in nltk/nltk versions <= 3.9.4 allows for cross-package resource and model poisoning. The downloader extracts package archives into shared namespaces such as `corpora/` and `taggers/` instead of package-isolated roots, and validates package integrity only after the archive has been written and extracted. This design flaw enables one package to overwrite another package's trusted resources within the same namespace, making the changes immediately active through ordinary NLTK APIs. This issue persists across fresh interpreter restarts and can affect downstream workflows, including machine learning pipelines and reproducibility-sensitive environments.
Title Improper Access Control in nltk/nltk
Weaknesses CWE-284
References
Metrics cvssV3_0

{'score': 5.3, 'vector': 'CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N'}
cve-icon MITRE

Status: PUBLISHED

Assigner: @huntr_ai

Published:

Updated: 2026-08-07T06:25:10.976Z

Reserved: 2026-06-15T10:13:29.195Z

Link: CVE-2026-12261

cve-icon Vulnrichment

No data.

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-07T07:30:09Z