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High, CVSS 7.5amended

Natural Language Toolkit (NLTK): URL-Encoded Path Traversal in nltk.data.load() Allows Arbitrary Local File Read

CVE-2026-54293GHSA-p4gq-832x-fm9v

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (nltk 3.10.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI nltk

    Affected
    <= 3.9.4
    Fixed in
    3.10.0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS
  • CVE-2026-54293: 0.63% estimated exploitation activity in the next 30 days; percentile 50.38 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary 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. Affected Component nltk/data.py — find(), normalizeresourceurl(), and the UNSAFENOPROTOCOLRE regex check. Relevant occurrences: data.py L650–L653 — final path constructed from url2pathname(resourcename) after checks data.py L54–L69 — UNSAFENOPROTOCOLRE operates only on the undecoded string data.py L219–L245 — normalizeresourceurl() for nltk:…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-p4gq-832x-fm9v

  2. Revision 1 · created ·

    Published from osv record GHSA-p4gq-832x-fm9v

Agent brief

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# Patch Next advisory brief: CVE-2026-54293

Advisory: Natural Language Toolkit (NLTK): URL-Encoded Path Traversal in nltk.data.load() Allows Arbitrary Local File Read
IDs: CVE-2026-54293, GHSA-p4gq-832x-fm9v
Record: https://patchnext.com/advisories/cve-2026-54293 (revision 2, source checked 26 Oct 2026, 13:49 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nltk 3.10.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI nltk: affected <= 3.9.4; fixed in 3.10.0

## Suggested inspection (read-only)
- `python -m pip show nltk`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nltk.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-p4gq-832x-fm9v (OSV record GHSA-p4gq-832x-fm9v lists affected ranges: PyPI nltk >=0 <3.10.0 (fixed))
- Verified: https://github.com/advisories/GHSA-p4gq-832x-fm9v (GitHub-reviewed advisory GHSA-p4gq-832x-fm9v lists affected ranges: PyPI nltk >=0 <=3.9.4)

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