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CVE-2025-14009 — Vulnerability in nltk — CVE Details

CRITICAL

NLTK has a Zip Slip Vulnerability

Published February 18, 2026Updated September 10, 2026Source: osv

Summary

A critical vulnerability exists in the NLTK downloader component of nltk/nltk, affecting all versions. The _unzip_iter function in nltk/downloader.py uses zipfile.extractall() without performing path validation or security checks. This allows attackers to craft malicious zip packages that, when downloaded and extracted by NLTK, can execute arbitrary code. The vulnerability arises because NLTK assumes all downloaded packages are trusted and extracts them without validation. If a malicious package contains Python files, such as __init__.py, these files are executed automatically upon import, leading to remote code execution. This issue can result in full system compromise, including file system access, network access, and potential persistence mechanisms.

Advisory Timeline

  • First published February 18, 2026 (236 days ago).
  • Last revised September 10, 2026 — 203 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

pip
Update nltk to 3.9.3 or later
pip install "nltk>=3.9.3"

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (1)

Affects 1 ecosystem: pypi (1).

PackageEcosystemAffectedFixed In
nltk
pypi
0.8, 0.9, 0.9.3, 0.9.4 (+59 more)3.9.3

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 10.0 score means for each attack dimension.

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

References

Frequently Asked Questions

What is CVE-2025-14009?
NLTK has a Zip Slip Vulnerability This vulnerability has been assigned a severity rating of CRITICAL (CVSS score: 10.0/10).
How do I check if my project is affected by CVE-2025-14009?
CVE-2025-14009 affects nltk. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2025-14009 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
10.0

Exploitation is straightforward and causes maximum impact. Patch immediately.

Also Known As

GHSA-7p94-766c-hgjp
PYSEC-2026-96

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