Description
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.
Severity (CVSS)
| Base score | 7.5 |
|---|---|
| Severity | High |
| Version | CVSS 3.1 |
| Vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N |
| Provided by | CNA |
Weaknesses
- CWE-22 — CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Affected products
| Vendor | Product | Versions |
|---|---|---|
| nltk | nltk | < 3.10.0-rc1 |
References
- https://github.com/nltk/nltk/security/advisories/GHSA-p4gq-832x-fm9v (x_refsource_CONFIRM)
- https://github.com/nltk/nltk/pull/3575 (x_refsource_MISC)
Generated from the official CVE List on 23 Jun 2026 10:05 UTC.