CVE-2026-126301 NLTK from 3.6 before 3.10.4 Quadratic CPU Exhaustion via LegalitySyllableTokenizer.tokenize

6.9 mediumEPSS 0.5%

Medium (6.9) in nltk nltk. EPSS 0.5% estimated probability of exploitation activity in the next 30 days.

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Affected
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NLTK from 3.6 before 3.10.4 contains an algorithmic complexity vulnerability in LegalitySyllableTokenizer.tokenize that allows remote attackers to exhaust CPU by supplying long all-vowel tokens. Attackers can submit a token such as a long run of vowels, causing the unguarded onset reversal loop to perform quadratic work and deny service to syllabification components.

Severity

CVSS 4.0

6.9 medium

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

CVSS 3.1

5.3 medium

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS: 0.5% estimated probability of exploitation activity in the next 30 days; 44th percentile. Scored 2026-11-13. A forecast for this CVE across the internet, not for your own systems.
CWE: CWE-407 Inefficient Algorithmic Complexity
Published: 2026-11-13 10:17 UTC
Modified: 2026-11-13 10:17 UTC
Assigned by: VulnCheck (CNA)
NVD analysis: Awaiting analysis
Record from: the NVD, synced 2026-11-13 10:42 UTC

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Affected

nltk:nltk

Versions

From the CNA's record in the CVE List.

Product	Affected
nltk	from 3.6 before 3.10.4

References

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