CVE-2026-12261 Details
Description
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.
A vulnerability exists in the NLTK downloader component of NLTK versions through 3.9.4, allowing for cross-package resource and model poisoning. The downloader extracts package archives into shared namespaces, such as 'corpora' and 'taggers', rather than into isolated package roots. Additionally, it validates package integrity only after extraction, creating a window for one package to overwrite another's trusted resources. This flaw can disrupt downstream workflows, including machine learning pipelines that rely on NLTK data integrity.
To address this vulnerability, NLTK should modify its package installation process to extract archives into package-specific roots, validate integrity before extraction, and implement atomic installation procedures that ensure partial or corrupted files are not left on disk.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Aug 7, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f | CISA-ADP | Permissions Required |
| https://huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f | [email protected] | Permissions Required |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-284 | Improper Access Control | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| nltk nltk | <= 3.9.4 |
CPE
Remediation
| |
Change History
3 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Sep 4, 2026 | Initial Analysis | [email protected] |
| Aug 7, 2026 | CVE Modified | CISA-ADP |
| Aug 7, 2026 | New CVE Received | [email protected] |