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No exploitation reportedFix availableAwaiting NVD analysis

CVE-2026-126298

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

No exploitation reported by the sources we read.

  • Published2026-11-13
  • Fixed in3.10.4
  • WeaknessCWE-400

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2026-11-1309:36CVE publishedCNA

Versions per branch

OSV
nltk
BranchAffectedFixed in
3.10< 3.10.43.10.4

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA1 product

As VulnCheck, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • nltkother versions: not affected
    Affected
    • < 3.10.4fixed in 3.10.4semver

    Not affected = 3.10.4

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-11-13

Fix

  1. Update nltk to 3.10.4

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Metasploit modules
none listed
Metasploit Framework

Sources

  • CISA-ADPSSVC decisionnone2026-11-13
  • CNACVSS 4.08.72026-11-13
  • CNACVSS 3.17.52026-11-13
  • NVDCVSS 3.17.5read 2026-11-13
  • CNAweakness (CWE)CWE-4002026-11-13
  • NVDweakness (CWE)CWE-400read 2026-11-13
  • OSVaffected packages—
  • GitHub AdvisoriesadvisoryHIGH2026-11-14

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 4.0 vector
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/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
Published
2026-11-13
Last Modified
2026-11-13
NVD status
Awaiting Analysis
GitHub Advisory
GHSA-6665-2vj3-h76r GHSA-r53h-rw34-8h97

Frequently asked questions

What is CVE-2026-126298?

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.

Is CVE-2026-126298 actively exploited?

Active exploitation of CVE-2026-126298 has not been confirmed.

What is the CVSS score for CVE-2026-126298?

CVE-2026-126298 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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