Executive brief
A critical security flaw has been identified in NLTK, a widely used library for processing human language data in Python applications. The library's downloader component fails to properly verify files when extracting them, allowing a malicious actor to provide a specially crafted package that executes unauthorized code on the host system. This could lead to a full system compromise, including the theft of sensitive data, unauthorized network access, or permanent control over the affected server.
Technical details
A Zip Slip vulnerability exists in the NLTK downloader component within the `_unzip_iter` function in `nltk/downloader.py`. The component utilizes `zipfile.extractall()` without performing adequate path validation or security checks on the contents of downloaded packages. An attacker can exploit this by crafting a malicious zip file containing Python files (such as `__init__.py`) designed to be extracted into sensitive directories. When these files are subsequently imported or executed by the system, it results in arbitrary code execution. The vulnerability is addressed in NLTK version 3.9.3.
Affected products
- NLTK Project NLTK All versions before 3.9.3
- Red Hat OpenShift AI 2.25
- Red Hat OpenShift Lightspeed unspecified
Timeline
- 2025-01-01: other: Initial tracking date in Red Hat VEX document
- 2026-02-18: disclosed: Vulnerability published via huntr.dev and NVD
- 2026-03-06: patched: NIST analysis notes fix in version 3.9.3
- 2026-04-23: patched: Red Hat released security advisory RHSA-2026:10184 for OpenShift AI