NLTK up to 3.10.3 has a path traversal flaw in its model‑artifact APIs. The flaw lets an attacker supply a caller‑controlled path that bypasses the library’s pathsec mechanism by invoking raw file operations. The result is that files outside the intended sandbox can be read or modified, giving an attacker read/write access to critical configuration or data files. This is a classic CWE‑22 Path Traversal weakness that undermines confidentiality and integrity of the host system.

The affected product is the NLTK library from the nltk organization, specifically all releases from the initial release through 3.10.3. Systems that import and use the TransitionParser, AveragedPerceptron, PerceptronTagger, or MaxEnt parameter APIs with pathsec enabled are impacted.

The CVSS score of 8.3 rates this as a high‑severity vulnerability. The EPSS score of <1% indicates a low exploitation probability, and the issue is not listed in the CISA KEV catalog. Attackers can exploit the flaw by invoking the vulnerable APIs over an exposed interface—such as a web service or a local script that imports NLTK—supply a crafted path, and then read or write files beyond the sandbox. Because the flaw operates through normal library functionality, no special conditions beyond using the affected APIs are required.