CVE-2026-126299

HIGH 7.5

NLTK before 3.10.4 Quadratic-Time Denial of Service via CCG Lexicon fromstring

CVSS Score

7.5

EPSS Score

0.0%

EPSS Percentile

0th

NLTK before 3.10.4 contains a denial of service vulnerability in the CCG lexicon parser fromstring that allows remote attackers to exhaust CPU by supplying wide inputs. Attackers can submit lexicon text with long flat bracket bodies or operator chains, triggering quadratic string re-slicing in matchBrackets and augParseCategory that blocks worker threads.

CWE	CWE-400
Vendor	nltk
Product	nltk
Published	Nov 13, 2026

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CVSS v3 Breakdown

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Affected Versions

nltk / nltk

0 < 3.10.4

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/nltk/nltk/security/advisories/GHSA-89p3-fcch-88ph vulncheck.com: https://www.vulncheck.com/advisories/nltk-before-3.10.4-quadratic-time-denial-of-service-via-ccg-lexicon-fromstring

Credits

🔍 manus-use