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High, CVSS 7.1amended

NLTK: FileSystemPathPointer.open() sandbox check is dead code — arbitrary file read via file:// protocol

CVE-2026-65915GHSA-72r2-7mfr-5xr9

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
    <= 3.9.3
    Fixed in
    3.10.0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
7.1 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X · score source
EPSS
  • CVE-2026-65915: 0.41% estimated exploitation activity in the next 30 days; percentile 35.33 (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 There's a logic bug in FileSystemPathPointer.open() inside nltk/data.py that makes the sandbox check permanently inert. The guard condition is always False — meaning any file the process can read is accessible by passing a file:// URL to nltk.data.load(). --- Details In nltk/data.py, FileSystemPathPointer.open() was patched at some point with a comment saying "SECURITY PATCH ENFORCING SANDBOX", but the check doesn't work: path is set to os.path.normpath(self.path) on line 1, then compared against os.path.normpath(self.path) again in the condition. They are always equal. The ValueError never fires. On top of that, init already calls os.path.abspath() before storing self.path, so it's normalized before open() is even called. Running normpath on it again changes nothing. The stream = open(self.path, "rb") line is always reached regardless of what path was passed in. --- PoC Tested on Python 3.11, NLTK 3.9.1, Ubuntu 22.04. Both print file contents. No exception is raised. ---…

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

    Amended from ghsa record GHSA-72r2-7mfr-5xr9

  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-72r2-7mfr-5xr9

  4. Revision 1 · created ·

    Published from ghsa record GHSA-72r2-7mfr-5xr9

Agent brief

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# Patch Next advisory brief: CVE-2026-65915

Advisory: NLTK: FileSystemPathPointer.open() sandbox check is dead code — arbitrary file read via file:// protocol
IDs: CVE-2026-65915, GHSA-72r2-7mfr-5xr9
Record: https://patchnext.com/advisories/cve-2026-65915 (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 7.1)
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 <= 3.9.3; 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-72r2-7mfr-5xr9 (GitHub-reviewed advisory GHSA-72r2-7mfr-5xr9 lists affected ranges: PyPI nltk >=0 <=3.9.3)
- Verified: https://osv.dev/vulnerability/GHSA-72r2-7mfr-5xr9 (OSV record GHSA-72r2-7mfr-5xr9 lists affected ranges: PyPI nltk >=0 <3.10.0 (fixed))

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