CVE-2026-12261

A vulnerability in `nltk.downloader` in nltk/nltk versions <= 3.9.4 allows for cross-package resource and model poisoning. The downloader extracts package archives into shared namespaces such as `corpora/` and `taggers/` instead of package-isolated roots, and validates package integrity only after the archive has been written and extracted. This design flaw enables one package to overwrite another package's trusted resources within the same namespace, making the changes immediately active through ordinary NLTK APIs. This issue persists across fresh interpreter restarts and can affect downstream workflows, including machine learning pipelines and reproducibility-sensitive environments.

CVSS v3 6.5 MEDIUM

6.5^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f	Permissions Required
https://huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f	Permissions Required

Configurations

Configuration 1 (hide)

cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-08-07 07:16

Updated : 2026-09-04 14:40

NVD link : CVE-2026-12261

Mitre link : CVE-2026-12261

CVE.ORG link : CVE-2026-12261

JSON object : View

Products Affected

nltk

nltk

CWE

CWE-284

Improper Access Control

{"id": "CVE-2026-12261", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-12261", "role": "CISA Coordinator", "options": [{"exploitation": "poc"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-08-07T15:25:29.448356Z"}}], "cvssMetricV30": [{"type": "Secondary", "source": "security@huntr.dev", "cvssData": {"scope": "UNCHANGED", "version": "3.0", "baseScore": 5.3, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N", "integrityImpact": "HIGH", "userInteraction": "REQUIRED", "attackComplexity": "HIGH", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "NONE"}, "impactScore": 3.6, "exploitabilityScore": 1.6}], "cvssMetricV31": [{"type": "Primary", "source": "nvd@nist.gov", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 6.5, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N", "integrityImpact": "HIGH", "userInteraction": "REQUIRED", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "NONE"}, "impactScore": 3.6, "exploitabilityScore": 2.8}]}, "affected": [{"source": "security@huntr.dev", "affectedData": [{"vendor": "nltk", "product": "nltk/nltk", "versions": [{"status": "affected", "version": "unspecified", "versionType": "custom", "lessThanOrEqual": "latest"}]}]}], "published": "2026-08-07T07:16:26.377", "references": [{"url": "https://huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f", "tags": ["Permissions Required"], "source": "security@huntr.dev"}, {"url": "https://huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f", "tags": ["Permissions Required"], "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "security@huntr.dev", "description": [{"lang": "en", "value": "CWE-284"}]}], "descriptions": [{"lang": "en", "value": "A vulnerability in `nltk.downloader` in nltk/nltk versions <= 3.9.4 allows for cross-package resource and model poisoning. The downloader extracts package archives into shared namespaces such as `corpora/` and `taggers/` instead of package-isolated roots, and validates package integrity only after the archive has been written and extracted. This design flaw enables one package to overwrite another package's trusted resources within the same namespace, making the changes immediately active through ordinary NLTK APIs. This issue persists across fresh interpreter restarts and can affect downstream workflows, including machine learning pipelines and reproducibility-sensitive environments."}], "lastModified": "2026-09-04T14:40:11.537", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "61FCC90A-0162-444E-922A-DDFBD189AD71", "versionEndIncluding": "3.9.4"}], "operator": "OR"}]}], "sourceIdentifier": "security@huntr.dev"}