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Medium, CVSS 6.8amended

NLTK: Symlink-based arbitrary file read in IPIPANCorpusReader, bypasses nltk.pathsec entirely

CVE-2026-62383GHSA-3hhw-38pf-pxj6

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (nltk 3.10.2), 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
    >= 3.10.0, < 3.10.2
    Fixed in
    3.10.2

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
6.8 · CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-62383: 0.18% estimated exploitation activity in the next 30 days; percentile 7.91 (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 IPIPANCorpusReader (nltk/corpus/reader/ipipan.py) exposes public methods, channels(), domains(), categories(), and fileids(channels=...), that accept a caller supplied fileids list and read a file via a completely unprotected builtin open() call, with no nltk.pathsec involvement at all. A symlink placed inside the corpus root, with a name containing no separators or .., passes NLTK's existing traversal checks and is opened directly, reading a file from anywhere on the filesystem the process can access. Root cause All four methods route through gettag(): f arrives via listheaderfiles() / listmorphfilesby(), both of which call: on the result of self.abspath(...) or self.abspaths(...). FileSystemPathPointer subclasses str, so .replace() returns a plain Python string, silently discarding the PathPointer wrapper. That plain string is handed straight to builtin open(). This is a more severe variant of the same CWE-59 class already fixed elsewhere in this codebase…

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

    Amended from ghsa record GHSA-3hhw-38pf-pxj6

  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-3hhw-38pf-pxj6

  4. Revision 1 · created ·

    Published from ghsa record GHSA-3hhw-38pf-pxj6

Agent brief

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# Patch Next advisory brief: CVE-2026-62383

Advisory: NLTK: Symlink-based arbitrary file read in IPIPANCorpusReader, bypasses nltk.pathsec entirely
IDs: CVE-2026-62383, GHSA-3hhw-38pf-pxj6
Record: https://patchnext.com/advisories/cve-2026-62383 (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: Medium (CVSS 6.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nltk 3.10.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI nltk: affected >= 3.10.0, < 3.10.2; fixed in 3.10.2

## 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-3hhw-38pf-pxj6 (GitHub-reviewed advisory GHSA-3hhw-38pf-pxj6 lists affected ranges: PyPI nltk >=3.10.0 <3.10.2)
- Verified: https://osv.dev/vulnerability/GHSA-3hhw-38pf-pxj6 (OSV record GHSA-3hhw-38pf-pxj6 lists affected ranges: PyPI nltk >=3.10.0 <3.10.2 (fixed))

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