CVE-2026-54293 — NLTK: URL-Encoded Path Traversal in nltk.data.load() Allows Arbitrary Local File Read

Description (CNA)

NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. Prior to 3.10.0-rc1, nltk.data.load() in NLTK is vulnerable to path traversal via URL-encoded path separators and traversal segments when using the nltk: URL scheme. The unsafe-path regex check is performed before url2pathname() decodes the %xx sequences (a classic decode-after-check / TOCTOU-style flaw), allowing an attacker to bypass the protection documented in NLTK's SECURITY.md and read arbitrary files from the filesystem. While literal traversal strings such as ../../../etc/passwd are correctly blocked, encoded variants such as %2fetc%2fpasswd, %2e%2e%2f..., and ..%2f..%2f slip past the regex and are subsequently decoded into a real filesystem path. This vulnerability is fixed in 3.10.0-rc1.

Affected (CNA)

Vendor / product	Versions
nltk / nltk	affected < 3.10.0-rc1

CWE

CWE-22

References

ADP enrichment

CISA-ADP

No English description supplied.

https://github.com/nltk/nltk/security/advisories/GHSA-p4gq-832x-fm9v

redhat-SADP

A flaw was found in NLTK (Natural Language Toolkit). The `nltk.data.load()` function is vulnerable to path traversal when processing specially crafted `nltk:` URLs. An attacker can exploit a decode-after-check flaw, where URL-encoded path separators and traversal segments bypass security checks. This allows the attacker to read arbitrary files from the filesystem, leading to information disclosure.