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CVE-2026-126298

NLTK before 3.10.4 Quadratic CPU Denial of Service via Tree.chomsky_normal_form

  • High 8.7

Description

NLTK before 3.10.4 contains a denial of service vulnerability in Tree.chomsky_normal_form that allows remote attackers to exhaust CPU through quadratic-time right-factor binarization using list.pop(0). Attackers can supply a wide flat treebank tree parsed by Tree.fromstring to force tens of seconds of single-threaded CPU consumption, blocking the processing thread.

Key facts

Published
13 Nov 2026
Last changed
13 Nov 2026
Assigned by
VulnCheck
EPSS
0.576% likely to be exploited in the next 30 days, higher than 48.069% of CVEs (scores for 15 Nov 2026)
SSVC (CISA)
Exploitation: none; Automatable: yes; Technical impact: partial

Severity scores

Each score is shown as its source gave it. They are not averaged or merged.

  • 8.7CVSS 4.0, Highfrom the CNA (VulnCheck)CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
  • 7.5CVSS 3.1, Highfrom the CNA (VulnCheck)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Historical context and remediation

This reference retains the original CVE publication date. A recent record update does not mean a new attack occurred.

No separately sourced impact summary is available on this page yet. Consult the description, version data and dated exploitation evidence.

No explicit remediation statement is available on this page yet. Consult the original record and vendor references before choosing a fix.

Version statuses below come from the CNA. An “unaffected” version is not necessarily a currently supported release or proof of a patch date. EPSS is a dated risk estimate, not a count of historical attacks.

Read the original CVE record.

Affected products

VendorProductVersions
nltknltk
  • Default status: unaffected
  • 0 up to but excluding 3.10.4 (affected)
  • 3.10.4 (unaffected)

Timeline

  1. 13 Nov 2026 Published

Weakness

References