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-2026-78681

CVE-2026-78681HIGH

NLTK before 3.10.3 Entity Expansion DoS via ElementTree

  AV  AC  AT  PR  UI  VC  VI  VA   CVSS    EPSS   %ile   KEV
   N   L   N   N   N   N   N   H    8.7   .0052   42.2     —

AFFECTED
  Product  Versions     Fixed
  nltk     unspecified  3.10.3

TIMELINE
  Aug 25  Reserved by VulnCheck
  Aug 25  Published (CNA: VulnCheck)
  Sep 1   EXPLOIT PUBLISHED — CVE-2026-78681 (nltk). Public exploit reference added.

CWE-776 · CNA: VulnCheck · CVSS v4.0 · 2 references · NVD status: Analyzed

Description

NLTK versions before 3.10.3 use xml.etree.ElementTree to parse XML in multiple modules, which honors entity declarations in document DTDs. Attackers can craft XML payloads with nested entity declarations that expand from hundreds of bytes to megabytes in memory, causing denial of service.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
August 25, 2026	Reserved	Reserved by VulnCheck
August 25, 2026	Published	Published (CNA: VulnCheck)
September 1, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-78681 (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-776

References (2)

https://github.com/nltk/nltk/security/advisories/GHSA-97qj-x29f-37w7 [Exploit, Vendor Advisory]
https://www.vulncheck.com/advisories/nltk-before-entity-expansion-dos-via-elementtree [Third Party Advisory]

Authoritative record: CVE-2026-78681 at cve.org

Vendors: nltk

Weaknesses: CWE-776

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-78681 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.