CVE-2026-81727

High

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.

SeverityHigh

CVSS7.1

Exploit probability—

ProductNltk

PublishedAug 27, 2026

First seenAug 27, 2026

Weakness typeCWE-59Improper link resolution

How to fix

Update

nltk nltk3.10.3 or later
nltk3.10.3 or later

Vendor advisories

github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672

Affected products

Product	Affected versions	Fixed in
nltk nltk	v < 3.10.3	3.10.3
nltkPyPI	v < 3.10.3	3.10.3

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