CVE-2026-81727: Nltk

High severity, CVSS 7.1. EPSS: 0.2% chance of exploitation in the next 30 days.

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.

Affected products

• Nltk Nltk: before 3.10.3 (fixed in 3.10.3)

Published 2026-08-27. Last modified 2026-08-31.