Natural Language Toolkit (NLTK): Path Traversal in NKJPCorpusReader leads to Arbitrary File Read and bypasses the nltk.pathsec sandbox (ENFORCE=True)

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

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Summary A path-traversal vulnerability in NKJPCorpusReader allows an attacker who can influence the fileids argument of its public read methods (header, raw, words, sents, taggedwords) to read files outside the corpus root. The reader builds the file path with no containment check and opens it with the builtin open(), so it bypasses NLTK's nltk.pathsec sandbox — including the strict ENFORCE = True mode that SECURITY.md recommends for web/multi-tenant deployments. header() returns the parsed content of the out-of-root file to the caller (arbitrary file read).

Details SECURITY.md promises that file access is "validated against allowed NLTK data directories" and that with nltk.pathsec.ENFORCE = True "unauthorized file access … will raise PermissionError." That guarantee is enforced via FileSystemPathPointer.open() / CorpusReader.open(), which call nltk.pathsec.validatepath(...). NKJPCorpusReader never uses that protected path. In nltk/corpus/reader/nkjp.py: - addroot() builds the…

Published by the source

31 Jul 2026, 16:50 UTC

Last modified by the source

31 Jul 2026, 16:50 UTC

Source last checked

26 Oct 2026, 13:50 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-6hm5-jgcp-p838

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# Patch Next advisory brief: CVE-2026-12072

Advisory: Natural Language Toolkit (NLTK): Path Traversal in NKJPCorpusReader leads to Arbitrary File Read and bypasses the nltk.pathsec sandbox (ENFORCE=True)
IDs: CVE-2026-12072, GHSA-6hm5-jgcp-p838
Record: https://patchnext.com/advisories/cve-2026-12072 (revision 1, source checked 26 Oct 2026, 13:50 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://github.com/advisories/GHSA-6hm5-jgcp-p838 (GitHub-reviewed advisory GHSA-6hm5-jgcp-p838 lists affected ranges: PyPI nltk >=0 <=3.9.4)

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