CVE-2026-81727

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.

Weakness classification

• disclosure@vulncheck.com: CWE-59

Primary references

• disclosure@vulncheck.com — Exploit, Vendor Advisory
• disclosure@vulncheck.com — Third Party Advisory
• 134c704f-9b21-4f2e-91b3-4a467353bcc0 — Exploit, Vendor Advisory