Open-source package vulnerability · PyPI

CVE-2025-14009: NLTK has a Zip Slip Vulnerability

criticalCVSS 3.0 10.0GHSA-7p94-766c-hgjp

A critical vulnerability exists in the NLTK downloader component of nltk/nltk, affecting all versions. The unzipiter 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.

Published Feb 18, 2026 · Updated Jun 6, 2026

Affected packages

nltk

Ecosystem: PyPI
Affected: <= 3.9.2
Fixed in: 3.9.3
Check: pip show nltk

Advisory details

From the GitHub Advisory Database (CC BY 4.0).

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.

Credited to leegks, adamlaurencik.

References

How this page is made: the data panel comes from the GitHub Advisory Database, CISA’s KEV catalog, the NVD and FIRST EPSS, and updates twice a day. No analysis has been written for this entry yet. Methodology

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