NLTK: Default ENFORCE=False Disables All pathsec Security Controls

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-62388: 0.51% estimated exploitation activity in the next 30 days; percentile 43.75 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

NLTK's pathsec.py security module defaults to ENFORCE=False (line 24), which means all 8 security validation functions only emit RuntimeWarning instead of raising exceptions when violations are detected. The pathsec module was introduced as the fix for CVE-2024-39705 (arbitrary code execution via pickle) and CVE-2026-0846 (path traversal). However, with ENFORCE=False as the default: 1. pathsec.open('/etc/passwd') succeeds (reads the file, emits warning) 2. pathsec.validatenetworkurl('http://169.254.169.254/...') succeeds (warning only) 3. pickle.loads() via nltk.data.load() proceeds despite unsafe source (warning only) Every security gate follows the same pattern: This means the security remediations for CVE-2024-39705 and CVE-2026-0846 are effectively disabled by default. Any user who installed NLTK 3.9.x expecting the security fixes to be active is still vulnerable unless they manually set NLTKPATHSECENFORCE=1. PoC: The correct default is fail-secure: ENFORCE should be True unless…

Published by the source

2 Sep 2026, 15:40 UTC

Last modified by the source

27 Oct 2026, 07:57 UTC

Source last checked

27 Oct 2026, 08:10 UTC

1. Revision 2 · amended · 27 Oct 2026

   Amended from ghsa record GHSA-p3m8-78j2-g5p3

2. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-p3m8-78j2-g5p3

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# Patch Next advisory brief: CVE-2026-62388

Advisory: NLTK: Default ENFORCE=False Disables All pathsec Security Controls
IDs: CVE-2026-62388, GHSA-p3m8-78j2-g5p3
Record: https://patchnext.com/advisories/cve-2026-62388 (revision 2, source checked 27 Oct 2026, 08:10 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
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-p3m8-78j2-g5p3 (GitHub-reviewed advisory GHSA-p3m8-78j2-g5p3 lists affected ranges: PyPI nltk >=0 <=3.9.4)

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