NLTK Path Traversal and Deserialization Bypass via ENFORCE=False

Executive Summary

CVE-2026-62388 affects NLTK versions before 3.10.0 due to an insecure default configuration in pathsec.py where ENFORCE is set to False. This causes security validation functions to only emit warnings instead of raising exceptions, effectively disabling protections against path traversal and pickle deserialization attacks.

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Detection Guidance

Check NLTK version with 'pip show nltk' or 'python -c "import nltk; print(nltk.__version__)"'. If version is below 3.10.0, the system is vulnerable. Inspect pathsec.py for ENFORCE=False default setting. Monitor for warnings in logs when accessing restricted paths or files.

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Impact Analysis

Attackers can exploit this to bypass security controls and access sensitive files or execute arbitrary code. For example, reading restricted files like /etc/passwd or performing unsafe deserialization could occur without proper warnings preventing the actions.

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Mitigation Strategies

Upgrade NLTK to version 3.10.0 or later. Set environment variable NLTK_PATHSEC_ENFORCE=1 to enable security controls. Review and restrict file access permissions. Monitor for suspicious file access attempts in logs.

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