---
id: CVE-2026-63312
title: >-
  NLTK before 3.10.0 contains an arbitrary local file read vulnerability in
  StreamBackedCorpusView that bypasses pathsec.ENFORCE by calling
  builtins.open() directly instead of pathsec.open()
summary: >-
  NLTK before 3.10.0 contains an arbitrary local file read vulnerability in
  StreamBackedCorpusView that bypasses pathsec.ENFORCE by calling
  builtins.open() directly instead of pathsec.open(). Attackers who control the
  fileid argument can r…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N'
cwe:
  - CWE-22
published: '2026-08-22'
updated: '2026-08-22'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63312'
references:
  - url: 'https://github.com/nltk/nltk/security/advisories/GHSA-x5ph-mj9p-rfr8'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/nltk-streambackedcorpusview-bypasses-pathsec-enforce-arbitrary-file-read
    label: disclosure@vulncheck.com
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63312'
  - url: 'https://github.com/nltk/nltk/pull/3588'
  - url: >-
      https://github.com/nltk/nltk/commit/674ea75accdf08eca3782dee0a9c4ed7e0d0025b
  - url: 'https://github.com/nltk/nltk/releases/tag/v3.10.0'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3730.yaml
  - url: 'https://github.com/advisories/GHSA-x5ph-mj9p-rfr8'
  - url: 'https://github.com/nltk/nltk'
tags:
  - nvd
  - ghsa
  - pip
  - osv
ingestedAt: '2026-08-23T04:42:15.353Z'
epss: 0.00651
epssPercentile: 0.4905
aliases:
  - GHSA-x5ph-mj9p-rfr8
  - PYSEC-2026-3730
ecosystem: pip
vendor: nltk
product: nltk
affected:
  - nltk <= 3.9.4
patched:
  - nltk 3.10.0
---

## Overview

NLTK before 3.10.0 contains an arbitrary local file read vulnerability in StreamBackedCorpusView that bypasses pathsec.ENFORCE by calling builtins.open() directly instead of pathsec.open(). Attackers who control the fileid argument can read arbitrary local files regardless of the ENFORCE setting, including sensitive system files and application credentials.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-63312)

Affected packages:

- `nltk <= 3.9.4`

Patched in:

- `nltk 3.10.0`

Source: https://github.com/advisories/GHSA-x5ph-mj9p-rfr8