High [CVE-2026-54293] Information Disclosure via Path Traversal in `nltk.data.load `

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.

An attacker can exploit a decode-after-check flaw, where URL-encoded path separators and traversal segments bypass security checks. This vulnerability is rated Important because a remote attacker may be able to read arbitrary local files on a system where an application passes untrusted input to nltk.data.load() using the nltk: URL scheme.

Exploitation requires an application that loads NLTK resources from attacker-influenced identifiers.