CVE-2026-126301
NLTK from 3.6 before 3.10.4 Quadratic CPU Exhaustion via LegalitySyllableTokenizer.tokenize
Published Nov 13, 2026
CVSS 4.0 · 6.9 Medium
EPSS n/a
KEV · Not listed
Description
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.
Analysis
Affected Products
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CVE record
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NVD configurations
No data
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Red Hat packages
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OpenCVE enrichment
No data
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| nltk | nltk | unaffected |
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No data available yet.
Remediation
Tracking
Advisories
Metrics
Attack Vector Network
Attack Complexity Low
Privileges Required None
Attack Requirements None
User Interaction None
Vulnerable System Confidentiality Impact None
Vulnerable System Integrity Impact None
Vulnerable System Availability Impact Low
Subsequent System Confidentiality Impact None
Subsequent System Integrity Impact None
Subsequent System Availability Impact None
Attack Vector Network
Attack Complexity Low
Privileges Required None
Scope Unchanged
Confidentiality Impact None
Integrity Impact None
Availability Impact Low
User Interaction None
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
No EPSS score available.
Key SSVC decision points have not yet been added.
References
History
Nov 13, 2026 9:45 AM
Description updated. Title updated. First appearance in the feed. Weaknesses updated. Affected versions updated. Affected vendors updated. Added references. Scoring metrics updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | NLTK from 3.6 before 3.10.4 Quadratic CPU Exhaustion via LegalitySyllableTokenizer.tokenize | |
| First Time appeared |
Nltk
Nltk nltk |
|
| Weaknesses | CWE-407 | |
| CPEs | cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Nltk
Nltk nltk |
|
| References |
| |
| Metrics |
cvssV3_1
|
Weaknesses
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CWE-407
Inefficient Algorithmic Complexity
Sources
Vulnrichment
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NVD
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Red Hat
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OpenCVE enrichment
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