---
id: CVE-2026-81723
title: >-
  NLTK versions before 3.10.3 contain a quadratic CPU exhaustion vulnerability
  in XMLCorpusView._read_xml_fragment() that rescans accumulated XML fragments
  on every 1 KiB block read
summary: >-
  NLTK versions before 3.10.3 contain a quadratic CPU exhaustion vulnerability
  in XMLCorpusView._read_xml_fragment() that rescans accumulated XML fragments
  on every 1 KiB block read. Attackers can provide malformed XML corpus files to
  caus…
severity: low
cvss: 3.7
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L'
cwe:
  - CWE-400
  - CWE-407
vendor: nltk
product: nltk
affected:
  - nltk < 3.10.3
patched:
  - nltk 3.10.3
published: '2026-08-27'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T20:44:42.207'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-81723'
references:
  - url: 'https://github.com/nltk/nltk/security/advisories/GHSA-vp2x-qp44-57v7'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/nltk-before-3.10.3-quadratic-cpu-exhaustion-via-xmlcorpusview
    label: disclosure@vulncheck.com
  - url: 'https://github.com/nltk/nltk/security/advisories/GHSA-vp2x-qp44-57v7'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-81723'
  - url: >-
      https://github.com/nltk/nltk/commit/7808692d451b962711005d954859bb83aabcf8fa
  - url: 'https://github.com/nltk/nltk'
  - url: 'https://github.com/nltk/nltk/releases/tag/v3.10.3'
  - url: 'https://pypi.org/project/nltk'
  - url: 'https://github.com/advisories/GHSA-vp2x-qp44-57v7'
tags:
  - nvd
  - osv
  - pip
  - ghsa
epss: 0.00281
epssPercentile: 0.18321
aliases:
  - GHSA-vp2x-qp44-57v7
  - PYSEC-2026-3871
ecosystem: pip
ingestedAt: '2026-09-02T14:45:30.348Z'
---

## Overview

NLTK versions before 3.10.3 contain a quadratic CPU exhaustion vulnerability in XMLCorpusView._read_xml_fragment() that rescans accumulated XML fragments on every 1 KiB block read. Attackers can provide malformed XML corpus files to cause severe CPU consumption and denial of service through affected readers like BNCCorpusReader.

## Remediation

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

## Package advisory (CVE-2026-81723)

Affected packages:

- `nltk < 3.10.3`

Patched in:

- `nltk 3.10.3`

Source: https://osv.dev/vulnerability/GHSA-vp2x-qp44-57v7