Reference page — cumulative record through Sunday, October 4, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-81727

CVE-2026-81727MEDIUM

NLTK before 3.10.3 Hardlink File Overwrite via downloader

  AV  AC  AT  PR  UI  VC  VI  VA   CVSS    EPSS   %ile   KEV
   L   L   N   L   N   N   H   H    6.9   .0019    7.5     —

AFFECTED
  Product  Versions     Fixed
  nltk     unspecified  3.10.3

TIMELINE
  Aug 27  Reserved by VulnCheck
  Aug 27  Published (CNA: VulnCheck)
  Aug 31  EXPLOIT PUBLISHED — CVE-2026-81727 (nltk). Public exploit reference added.

CWE-59 · CNA: VulnCheck · CVSS v4.0 · 2 references · NVD status: Analyzed

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.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
August 27, 2026	Reserved	Reserved by VulnCheck
August 27, 2026	Published	Published (CNA: VulnCheck)
August 31, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-81727 (nltk). Public exploit reference added.

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
nltk	nltk	—	—	3.10.3

Weaknesses

CWE-59

References (2)

https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672 [Exploit, Vendor Advisory]
https://www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-downloader [Third Party Advisory]

Authoritative record: CVE-2026-81727 at cve.org

Vendors: nltk

Weaknesses: CWE-59

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-81727 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Sunday, October 4, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.