NLTK versions prior to 3.10.0 default to ENFORCE=False in the pathsec module, causing all security validation functions to emit only warnings instead of raising exceptions. This flaw allows an attacker to bypass built‑in path traversal checks and the protections against malicious pickle deserialization, potentially enabling arbitrary file access or code execution if a vulnerable application processes user supplied paths or pickle data.

The vulnerability affects the NLTK library published by the nltk project, all releases before 3.10.0. Any Python application that imports and uses NLTK in those versions is potentially exposed.

The flaw is scored with a CVSS score of 8.7, indicating high severity. No EPSS value is currently provided, and the vulnerability is not listed in the CISA KEV catalog. The attack vector is inferred from the description: any code path that supplies a file location or pickle payload to NLTK functions can trigger the warning‑only behaviour and bypass security checks; this can be local or remote depending on the application context.