CVE-2026-81727CWE-59

CVE-2026-81727

High · published August 27, 2026

CVSS v3.1
7.1
EPSS
0%
Percentile
7.9
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
7.1 · HIGH
Vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
CVSS v4.0
6.9 · CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
EPSS
0.00187 · 7.9th percentile
Weakness
CWE-59 · Improper Link Resolution Before File Access ('Link Following')
Published
2026-08-27T21:21Z
Affected products (1)
ProductVersionsFixed in
nltk/nltk< 3.10.33.10.3
References (3)
https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672 · [email protected]https://www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-downloader · [email protected]https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672 · 134c704f-9b21-4f2e-91b3-4a467353bcc0
EPSS history
Timeline
  • 27 AUG 14:51Z
    NLTK before 3.10.3 Hardlink File Overwrite via downloader
    cvelistv5