Vulnerability in Nltk
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 · last modified .
CVSS v3 metric
CVSS v3 base score 7.1 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H.
EPSS exploit prediction
EPSS: 0.002 (7.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 8th percentile — 7.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.001 · newest: 0.002 · change: +0.001
Affected products
Weakness classification (CWE)
References
- github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672 (Exploit, vendor-advisory, Vendor Advisory)
- www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-dow… (Third Party Advisory, third-party-advisory)
Frequently asked questions
- What is CVE-2026-81727?
- CVE-2026-81727 is a high-severity vulnerability in Nltk, classified under Improper Link Resolution Before File Access. CVSS score: 7.1/10. Published 2026-08-27.
- How severe is CVE-2026-81727?
- High severity. CVSS v3 base score is 7.1 out of 10.