NLTK through 3.10.3 contains a path traversal vulnerability in model-artifact APIs that bypass pathsec enforcement by using raw file operations on caller-controlled paths. Attackers can read or write files outside allowed sandbox roots through TransitionParser, AveragedPerceptron, PerceptronTagger, and maxent parameter APIs when pathsec is enabled.

NLTK versions through 3.10.3 contain a path traversal vulnerability in model-artifact APIs that bypass pathsec enforcement by using raw file operations on caller-controlled paths. The vulnerability affects TransitionParser, AveragedPerceptron, PerceptronTagger, and maxent parameter APIs. Attackers can exploit this flaw to read or write files outside allowed sandbox roots even when pathsec is enabled. The issue stems from the use of raw file operations on caller-controlled paths rather than properly sanitized paths. This represents a significant security risk for applications that rely on NLTK's pathsec mechanism for sandbox enforcement. The vulnerability has been assigned CVE-2026-81726 and is documented in both the NVD and GitHub Security Advisories. Organizations using NLTK for natural language processing tasks should prioritize patching or mitigating this vulnerability.