Improper Validation of Integrity Check Value Affecting nltk package, versions [,3.10.0)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-NLTK-19639601
- published7 Sept 2026
- disclosed3 Aug 2026
- creditUnknown
Introduced: 3 Aug 2026
CVE-2026-12259 (opens in a new tab)How to fix?
Upgrade nltk to version 3.10.0 or higher.
Overview
nltk is a Natural Language Toolkit (NLTK) is a Python package for natural language processing.
Affected versions of this package are vulnerable to Improper Validation of Integrity Check Value in nltk/downloader.py through the Downloader._download_package() download-and-extract flow. An attacker can install malicious package contents by tampering with the archive response, such as through a compromised mirror, HTTP interception, or a substituted download source. The downloader writes the fetched package to disk and then proceeds to extract it without verifying the final file against the expected checksum, so a modified archive can be unpacked as if it were trusted. This can lead to attacker-controlled corpus or model files being installed on systems that use nltk.download().