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CVE-2026-81727 Details

Description

NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incr_download methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader directory can create hardlinks pointing to outside-root files that are then overwritten during normal package extraction, mutating files outside the intended install tree.

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: [email protected]CVSS-B:7.1 HIGHVector:CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672	CISA-ADP	ExploitVendor Advisory
https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672	[email protected]	ExploitVendor Advisory
https://www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-downloader	[email protected]	Third Party Advisory

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-59	Improper Link Resolution Before File Access ('Link Following')	[email protected]

Affected Products

Product	Versions
nltk nltk	< 3.10.3
CPE cpe:2.3:a:nltk:nltk:::::::: Remediation No remediation found in references.

Change History

3 change records found show changes

Date	Action	Recorded By
Aug 31, 2026	Initial Analysis	[email protected]
Aug 27, 2026	CVE Modified	CISA-ADP
Aug 27, 2026	New CVE Received	[email protected]