CVE-2026-54293

Vulnerability 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.

CVSS Score

Affected Products

Related Weaknesses (CWE)

References

• https://github.com/nltk/nltk/pull/3575Issue TrackingPatch
• https://github.com/nltk/nltk/security/advisories/GHSA-p4gq-832x-fm9vExploitVendor Advisory
• https://access.redhat.com/errata/RHSA-2026:42644
• https://access.redhat.com/security/cve/CVE-2026-54293
• https://bugzilla.redhat.com/show_bug.cgi?id=2491486
• https://github.com/nltk/nltk/security/advisories/GHSA-p4gq-832x-fm9vExploitVendor Advisory
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-54293.json