Remote Code Execution Vulnerability in NLTK by NLTK

CVE-2026-79657

What is CVE-2026-79657?

Versions of NLTK prior to 3.10.3 include a significant remote code execution vulnerability that arises from their handling of allowlisted pickle loaders. These loaders trust entire module namespaces instead of restricting access to specific safe callables. This flaw allows attackers to craft malicious pickle payloads that can invoke potentially harmful functions from the namespace during the loading of model or tokenizer artifacts. Notably, functions like ReppTokenizer._execute and numpy.f2py.crackfortran.myeval can be exploited through the pickle REDUCE, enabling arbitrary command execution.

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