Information Disclosure via Path Traversal in `nltk.data.load()`

Summary

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. 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. 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. Many Red Hat products ship nltk as a bundled dependency without exposing this code path to untrusted input. Affected packages should be updated to nltk 3.10.0 or later when fixes are released. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N). Weakness: CWE-22. No fixing RHSA erratum has published yet; monitor the Red Hat CVE page and patch when it ships. Will not fix / out of support: Red Hat Ansible Automation Platform 2.