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High, CVSS 8.8amended

NLTK: Corpus Reader Sandbox Bypass

CVE-2026-79674GHSA-3gq4-3j92-5w49

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (nltk 3.10.3), 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
    <= 3.10.2
    Fixed in
    3.10.3

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
8.8 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-79674: 0.39% estimated exploitation activity in the next 30 days; percentile 32.87 (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 corpus-reader constructors can still reach outside-root file and database reads before the nltk.pathsec sandbox boundary is enforced. The PoC shows the safe path blocked by pathsec.open, then LinThesaurusCorpusReader and PanLexLiteCorpusReader succeeding in the same process. Affected Product - Product: NLTK - Asset / component: nltk.corpus.reader constructors - Version tested: 3.10.2 - Deployment / package / tag: commit 474af1f5a94b1b8d53fc2b6defec3a2ce7633b74 / PyPI nltk - Environment used for verification: Python 3.13.14 Vulnerability Details - Vulnerability class: path sandbox bypass / external control of file path - Required privileges: none beyond the ability to supply a corpus root path to a consumer call site - Entry point: LinThesaurusCorpusReader(root) and PanLexLiteCorpusReader(root) - Trust boundary crossed: NLTK data-root sandbox enforced by nltk.pathsec - Root affected functions: - CorpusReader.init - LinThesaurusCorpusReader.init -…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from ghsa record GHSA-3gq4-3j92-5w49

  2. Revision 3 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 2 · amended ·

    Amended from osv record GHSA-3gq4-3j92-5w49

  4. Revision 1 · created ·

    Published from ghsa record GHSA-3gq4-3j92-5w49

Agent brief

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# Patch Next advisory brief: CVE-2026-79674

Advisory: NLTK: Corpus Reader Sandbox Bypass
IDs: CVE-2026-79674, GHSA-3gq4-3j92-5w49
Record: https://patchnext.com/advisories/cve-2026-79674 (revision 4, source checked 26 Oct 2026, 13:51 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nltk 3.10.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI nltk: affected <= 3.10.2; fixed in 3.10.3

## 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-3gq4-3j92-5w49 (GitHub-reviewed advisory GHSA-3gq4-3j92-5w49 lists affected ranges: PyPI nltk >=0 <=3.10.2)
- Verified: https://osv.dev/vulnerability/GHSA-3gq4-3j92-5w49 (OSV record GHSA-3gq4-3j92-5w49 lists affected ranges: PyPI nltk >=0 <3.10.3 (fixed))

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