---
id: CVE-2026-78682
title: >-
  NLTK before 3.10.3 contains a server-side request forgery vulnerability in
  nltk.pathsec.urlopen (and callers nltk.data.load,
  nltk.downloader.Downloader.index/download) when an HTTP proxy is configured
summary: >-
  NLTK before 3.10.3 contains a server-side request forgery vulnerability in
  nltk.pathsec.urlopen (and callers nltk.data.load,
  nltk.downloader.Downloader.index/download) when an HTTP proxy is configured.
  pathsec.urlopen validates the reque…
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-918
  - CWE-441
vendor: nltk
product: nltk
affected:
  - nltk < 3.10.3
patched:
  - nltk 3.10.3
published: '2026-08-25'
updated: '2026-10-12'
sourceUpdated: '2026-10-12T21:10:00.227'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-78682'
references:
  - url: 'https://github.com/nltk/nltk/security/advisories/GHSA-6ww7-3frv-cqxh'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/nltk-before-ssrf-protection-bypass-via-proxy
    label: disclosure@vulncheck.com
  - url: 'https://github.com/nltk/nltk/security/advisories/GHSA-6ww7-3frv-cqxh'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-78682.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-78682'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2523191'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-78682'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-78682'
  - url: 'https://access.redhat.com/errata/RHSA-2026:73987'
  - url: >-
      https://github.com/nltk/nltk/commit/767333a005a1cd3d82d2029215f2dbe66a5844d9
  - url: 'https://github.com/nltk/nltk'
  - url: 'https://github.com/nltk/nltk/releases/tag/v3.10.3'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3733.yaml
  - url: 'https://github.com/advisories/GHSA-6ww7-3frv-cqxh'
  - url: 'https://access.redhat.com/errata/RHSA-2026:84734'
tags:
  - nvd
  - cve.org
  - exploit-available
  - csaf
  - vex
  - red-hat
  - osv
  - pip
  - ghsa
epss: 0.00435
epssPercentile: 0.37575
aliases:
  - GHSA-6ww7-3frv-cqxh
  - PYSEC-2026-3733
ecosystem: pip
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-08-25T15:23:28.158842Z'
ingestedAt: '2026-09-02T19:31:24.306Z'
---

## Overview

NLTK before 3.10.3 contains a server-side request forgery vulnerability in nltk.pathsec.urlopen (and callers nltk.data.load, nltk.downloader.Downloader.index/download) when an HTTP proxy is configured. pathsec.urlopen validates the requested hostname locally, but proxy-handler inheritance disables the safe HTTP/HTTPS handlers so the actual fetch is performed by the proxy against a destination that is never re-validated. An attacker can supply a validated public URL that the proxy forwards to an internal loopback-only service, allowing disclosure of internal HTTP resources, loading of forged downloader indexes, and installation of attacker-chosen package content.

## Affected

- `nltk < 3.10.3`

## Remediation

Upgrade past the affected range:

- `nltk 3.10.3`

## Package advisory (CVE-2026-78682)

Affected packages:

- `nltk < 3.10.3`

Patched in:

- `nltk 3.10.3`

Source: https://osv.dev/vulnerability/GHSA-6ww7-3frv-cqxh

## Vendor advisories

- **RHSA-2026:73987** · Red Hat · fixed in: Red Hat OpenShift AI 3.3 · released 2026-09-30 · [advisory](https://access.redhat.com/errata/RHSA-2026:73987)
- **Red Hat VEX** · Important · affected: Exploit Intelligence, Lightspeed Core, OpenShift Lightspeed, Red Hat Ansible Automation Platform 2, Red Hat OpenShift AI (RHOAI) · no fix planned: Exploit Intelligence, Red Hat Ansible Automation Platform 2, Lightspeed Core, OpenShift Lightspeed, … · updated 2026-10-19 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-78682.json)
- **RHSA-2026:84734** · Red Hat · fixed in: Red Hat OpenShift AI 3.4 · released 2026-10-19 · [advisory](https://access.redhat.com/errata/RHSA-2026:84734)