Cross-Package Resource Poisoning in NLTK by NLTK

CVE-2026-12261

What is CVE-2026-12261?

A vulnerability exists in the NLTK downloader component that enables cross-package resource and model poisoning. This occurs because the downloader extracts package archives into shared directories such as 'corpora/' and 'taggers/'. Package integrity checks are only performed after the archive is fully extracted, allowing one package to overwrite the resources of another in the same namespace. As a result, any modifications made are immediately available through standard NLTK APIs. This flaw can have significant implications, especially in machine learning pipelines and environments requiring reproducibility, as it affects workflows even after restarting the interpreter.

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