CVE-2026-81727
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.
- Published Aug 27, 2026
- CVSS 6.9 medium
- 0.2% chance of exploitation in the next 30 days (EPSS)
- Public exploit code is available
- A fix is available