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VulnerabilityPublished

CVE-2026-126298: nltk · Uncontrolled Resource Consumption

Affects nltkSource CVE Database V5

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Not known to be exploited · CVSS 8.7 High : upgrade to 3.10.4 soon.

Data as of 13 Nov 2026, 09:59 UTC

CVSS 4.0 base score
8.7High
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (VulnCheck)CVSS 4.08.7
CNA (VulnCheck)CVSS 3.17.5
Patch
Available – fixed in 3.10.4
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

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 13 Nov 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

What to do

Upgrade nltk to 3.10.4.

Affected software

ProductAffectedFixed in
nltknltkAffected
  • <3.10.4
Fixed in
  • 3.10.4
PyPInltkpkg:pypi/nltkOther threatsAffected
  • <3.10.4
Fixed in
  • 3.10.4

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

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.

References

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